Genetic Processes - 1

Question 1

What is genetic material?

Answer 1

Material in an organism that stores information.

Question 2

What is DNA? What does it stand for?

Answer 2

Molecules which carry genetic information in cells. Deoxyribonucleic Acid.

Question 3

What is a gene?

Answer 3

A portion of DNA that carries the information which codes for a specific trait.

Question 4

Traits of chromosomes

Answer 4

Found in eukaryotic cell nuclei

Contain genes

Most occur in sets; humans have 23 pairs

Question 5

Chromosomes in mitosis

Answer 5

Before replication, each chromosome is single stranded (one chromatid)

After duplication, the chromosomes are made up of two identical sister chromatids held together by a centromere

During mitosis, sister chromatids will separate from each other

One chromatid will end up in each daughter cell

IMPORTANT NOTE. Sister chromatids are still counted as one chromosome, just as one chromatid is counted as one chromosome. When your cells are getting ready to divide, they have 46 chromosomes and 92 chromatids, because there are two chromatids in each chromosome (double the normal amount)

Question 6

Why does DNA replicate?

Answer 6

DNA replicates so that, during mitosis, newly formed cells each receive a complete copy of genetic information.

Question 7

What are karyotypes?

Answer 7

A picture of the number and appearance of chromosomes in the nucleus of a eukaryotic cell.

Question 8

Differing human karyotypes: sex chromosomes

Answer 8

Human females have two X chromosomes, whereas males have one X and one Y.

Biological sex is assigned at birth and refers to someone’s physical anatomy/genetic characteristics.

Question 9

What is intersex?

Answer 9

Intersex is the term for people who are not born with a typical reproductive or sexual anatomy.

Some of their cells may have XX while others may have XY, which is called mosaic genetics

Question 10

What is the purpose of mitosis?

Answer 10

The purpose of mitosis is to maintain genetic continuity. This means the number of chromosomes in each daughter cell stays the same.

Question 11

What are the parts of interphase?

Answer 11

G1 – Cellular contents, excluding chromosomes, are duplicated

S – Each of the 46 chromosomes is duplicated

G2 – The cell “double checks” for errors in the duplicated chromosomes, fixing any mistakes

Question 12

What are diploid cells?

Answer 12

The number of chromosomes in body cells is twice the haploid number, or 2n. In humans, this number is 46.

Question 13

What are haploid cells?

Answer 13

The number of chromosomes in a gamete is called the haploid number, or the n. In humans, this number is 23.

Question 14

What is a gamete?

Answer 14

A gamete is a reproductive cell of an animal or plant. In animals, female gametes are called ova or egg cells, and male gametes are called sperm.

Question 15

What are the parts of mitosis, and what happens in each stage?

Answer 15

Prophase

Centrioles move to opposite poles of the cell

Chromatin condenses and shortens into chromosomes

Spindle fibres form between the centrioles

Nuclear membrane begins to disappear

Metaphase

Spindle fibres attached to centromeres pull chromosomes into place

Chromosomes line up across the equator of the cell

Centromeres duplicate

Anaphase

Chromatids separate at their centromeres

Single-stranded chromosomes are now pulled to opposite poles by spindle fibres contracting

Telophase

Two nuclear envelopes form

Single stranded chromosomes uncoil to become chromatin

Question 16

What happens in cytokinesis?

Answer 16

Organelles are distributed between daughter cells and cell membrane pinches inward

2 Daughter cells are formed

Question 17

What is the purpose of meiosis?

Answer 17

Purpose is to produce haploid gametes, which each hold half the amount of chromosomes as normal

They unite during sexual reproduction

(the number of chromosomes in each cell is half of the parent’s cell)

Produces 4 cells which are not identical

Question 18

Sexual vs asexual reproduction

Answer 18

Asexual reproduction

Gives rise to offspring which are completely genetically identical to the parent
Often produces offspring rapidly

Sexual Reproduction

Genetic information from two cells is combined to produce a new organism
Requires more time and energy from the organism
Offspring are genetically different from parents
Offspring are better able to adapt to changing environments

Question 19

What is a homologous pair (of chromosomes)?

Answer 19

Matching pairs of chromosomes that carry information for the same genes. Similar, but not genetically identical.

Question 20

What is a sister chromatid?

Answer 20

Refers to either of the two chromatids formed by the replication of a single chromosome; identical pair

Question 21

What are the stages of meiosis?

Answer 21

(Meiosis I)
Prophase I
Metaphase I
Anaphase I
Telophase I
(Meiosis II)
Prophase II
Metaphase II
Anaphase II
Telophase II

Question 22

What happens during prophase I in meiosis?

Answer 22

Chromatin condenses and becomes visible

Nuclear membrane disappears

Chromosomes come together in homologous pairs

Each chromosome is referred to as sister chromatids, and all four are referred to as a tetrad because there is four chromatids in a pair of homologous chromosomes

Pieces of the homologous pairs break off and exchange segments with other strands.

This process is called crossing over or genetic recombination

Centrioles duplicate

Question 23

What happens in metaphase and anaphase I in meiosis?

Answer 23

Metaphase I

Centrioles move to the poles

Spindle fibres attach to the centromeres

Homologous pairs are pulled to the equator by spindle fibres

Anaphase I

Spindle fibres contract, pulling homologous pairs apart

Double stranded pairs are pulled to opposite poles. They are not being pulled into single stranded chromosomes.

Only one chromosome from each pair will be in each cell

Question 24

What happens in telophase I in meiosis?

Answer 24

The homologous pair of chromosomes are fully separated

The nuclear membrane re-appears

Centrioles and spindle fibres disappear

Sister chromatids stay together, forming two haploid cells. The original cell had 4 chromosomes, and 2 were pulled into each cell.

Question 25

How does meiosis II look?

Answer 25

Meiosis II proceeds like mitosis, but with half the number of chromosomes.

Question 26

What is the final product of meiosis?

Answer 26

Cells are not identical because of independent assortment

Homologous chromosomes could have split in any order

The more chromosomes in a cell, the more possibilities come from independent assortment

For any diploid organism, the number of combinations is 2^n.

Also different from genetic recombination

Question 27

What is meiosis in males and females called?

Answer 27

When meiosis occurs in males it is called spermatogenesis because sperm are produced.

When meiosis occurs in males it is called Oogenesis because ova are produced.

Question 28

What are autosomal chromosomes?

Answer 28

chromosomes which carry genes for non-sexual characteristics.

Question 29

What do the sex chromosomes do?

Answer 29

determine an individual’s biological sex and carry genes which code for sexual characteristics.

The Y chromosome carries genes for facial hair, while the X chromosome codes for many non-sexual characteristics. This is because humans are automatically born female (e.g., all “sex characteristics” are added on by the Y chromosome)

Question 30

What is nondisjunction?

Answer 30

occurs when a homologous pair fails to properly separate during cell division.

This means both move to the same side of the cell, resulting in one daughter cell with an extra chromosome and one with a missing chromosome.

Cells with too much or not enough information cannot function properly.

While nondisjunction can happen in mitosis, it is much more serious in meiosis.

Resulting offspring will have either 45 or 47 chromosomes in each cell.

Question 31

Trisomy

Answer 31

Having an extra chromosome is known as trisomy, because individuals will have 3 homologous chromosomes in place of a pair

Question 32

Monosomy

Answer 32

Having a missing chromosome is known as monosomy, because individuals will have one chromosome in place of a pair of a homologous pair.

Question 33

Down Syndrome

Answer 33

Trisomy results in the disorder Down Syndrome, where there is an extra 21st chromosome. It occurs in 1 in 600 babies.

The chance of giving birth to a child with down syndrome increases as a mother gets older, because the occurrence of nondisjunction in the ova increases with age.

Question 34

Turner Syndrome

Answer 34

Monosomy where the only sex chromosome inherited is the X chromosome is known as Turner Syndrome.

1 in 3000 female births, with most babies being miscarried.

Question 35

Klinefelter Syndrome

Answer 35

Trisomy also results in Klinefelter Syndrome, where a baby is born with two X chromosomes and one Y chromosome.

Child appears male at birth but produces female hormones as they mature

Can develop breasts/have little facial hair

1 in 500 male births, with children being sterile.

Question 36

Heredity definition

Answer 36

The passing of traits from a parent to their offspring.

Question 37

What is heredity?

Answer 37

You inherit half of your chromosomes from your mother and half from your father (23 each). Your physical traits are a result of this interaction.

Biological traits are coded for by genes which are located on the chromosomes in your body.

A trait is the particular version of a characteristic that is inherited, such as hair or eye colour.

The idea that traits are inherited (heritable) has been known for centuries, and early communities would selectively mate for certain desirable traits to eliminate offspring with undesirable traits.

Question 38

What was blending theory?

Answer 38

This was the idea that traits from parents would blend together completely. This cannot be true, because it would mean that variation does not occur, but we see that it does.

Question 39

Who is Gregor Mendel?

Answer 39

Preformed classic experiments using garden pea plants.

Provided the basis of our current understanding of inheritance.

Question 40

What were Mendel’s experiments?

Answer 40

His first experiment was to crossbreed pure tall and pure short breeds. These plants were known as the parental generation (P)

This experiment is called a monohybrid cross because it focuses on only one inherited characteristic.

His hypothesis was that the offspring of the parental generation was going to be of medium height.

What he found instead was that all offspring, called first filial generation (F1) of the P generation was tall.

His conclusion was that the trait of being tall is dominant, while shortness is recessive, because the recessive trait was not seen at all in the first generation of offspring.

Medel’s Second Experiment:

The offspring of the F1 generation was called F2.

¾ of the F2 ended up being short, even though all of the F1 generation was tall.

His conclusion from this was that offspring inherit both the dominant and recessive traits of their parents, but only the dominant factor is expressed. The recessive trait is still there and has a chance to come out in another generation.

Hereditary characteristics are determined by distinct genes that occur in pairs. These paired factors separate from one another and are distributed into different sex cells.

Question 41

What is the principal of dominance?

Answer 41

When an organism is crossed for a pair of contrasting traits, it shows only the dominant trait.

Question 42

What is the law of segregation?

Answer 42

From Mendel’s data, he came to the following conclusions:

For each characteristic, an organism carries two factors; one from each parent.

Parent organisms donate only one copy of each gene in their gametes. During meiosis, the two copies of each gene separates.

Question 43

What are alleles?

Answer 43

Alleles are different forms of a gene

Different alleles arise by mutation

E.g., The gene for eye colour has different alleles: brown or blue

Dominant alleles are indicated with capital letters, recessive alleles are indicated with lower case letters.

You have two alleles for each trait, one from both parents.

If you inherit a dominant allele from one parent and a recessive allele from your other, the dominant allele will mask the recessive allele. This means you will only show the dominant allele.

If you are showing a recessive trait, it means you inherited two copies of it. If you are showing a dominant trait, you could have inherited one or both copies of it.

Question 44

Heterozygous vs Homozygous

Answer 44

Homozygous

Having two identical alleles for a gene

AA/aa

Heterozygous

Having two different alleles for a gene

Aa

Question 45

Genotype vs Phenotype

Answer 45

Genotype

The exact alleles an individual carries.

Someone with brown eyes may have BB or Bb as their genotype.

Phenotype

The observable traits in an offspring.

The phenotype of someone with brown eyes is just brown eyes.

Question 46

What is the law of independent assortment?

Answer 46

Alleles of different genes assort independently of one another during gamete formation, so different traits are inherited independently of each other.

In other words, the ability to have a dominant allele for one trait doesn’t affect your ability to receive a dominant allele in another, because each chromosome with each gene assorts itself randomly.

Question 47

What is a Punnett Square?

Answer 47

A Punnett Square is used to predict the proportions of genotypes in offspring resulting from a cross of two individuals. Can focus on one trait, or on many.

Question 48

Steps to solving a monohybrid cross problem

Answer 48

Determine the possible gametes from each parent

Draw a Punnett Square for each monohybrid cross

Execute the cross

Question 49

Monohybrid cross

Answer 49

A monohybrid cross focuses on one inherited characteristic.

Question 50

Fertilization

Answer 50

two gametes joining together to form one cell (zygote) with 2n chromosomes.

Question 51

Somatic cells

Answer 51

any cells in the body which are not gametes.

Question 52

Reproduction

Answer 52

producing offspring

Question 53

Genetic Recombination (/Crossing over)

Answer 53

the rearrangement of DNA sequences by the breakage and rejoining of chromosomes or chromosome segments.

Question 54

Independent assortment

Answer 54

the alleles of two (or more) different genes get sorted into gametes independently of one another.

Question 55

Gametogenesis

Answer 55

the process by which gametes are formed for sexual reproduction.

Question 56

Non disjunction

Answer 56

the failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of chromosomes