Lecture Notes: Lesson 1 and Lesson 2

Question 1

What is Mendel’s first law?

Answer 1

Independent assortment –> Mendel’s first law applies to a genetic cross to monitor the segregation of a single gene with allele

Question 2

Describe Mendel’s first law:

Answer 2

The key concept is that crosses or mating between parents with known genotypes produces offspring with different genotypes and phenotypes at predictable frequencies or ratios.

Question 3

Genotypes describes:

Answer 3

The alleles that an individual carries

Question 4

Phenotype describes:

Answer 4

The appearance of the individual (this may include physical appearance or characterization at the biochemical level)

Question 5

Diploid organisms:

Answer 5

Carry two copies of each gene

Question 6

Genes can have variants, each variant is called an ___

Answer 6

Allele
(example: the blue and brown alleles of the human eye colour gene)

Question 7

If we consider one gene, a
HETEROZYGOTIC individual carries:

Answer 7

Two different variants of the gene

Question 8

When a heterozygotic individual produces gametes (egg,sperm or pollen), each gamete has a ___ chance of receiving a particular allele of the gene

Answer 8

50/50

Question 9

The fusion of two gametes is __ relative to the alleles that they carry

Answer 9

random

Question 10

A cross between two heterozygotes results in offspring:

Answer 10

AA, Aa, aa
1:2:1 genotypic ratio
3:1 phenotypic ration

Question 11

A result between a heterozygote and a homozygote:

Answer 11

Aa, aa
1:1 genotypic ratio
1:1 phenotypic ratio

Question 12

if we know the genotypes of the parents, we can predict ___ of the offspring

Answer 12

The genotypic AND phenotypic ratios

Question 13

if we know the phenotypic ratio of the offspring, we can often decipher the __ of the parents

Answer 13

genotypes

Question 14

Define test-cross:

Answer 14

A test-cross is a cross of a homozygous recessive individual (aa) known as the tester to any other individual.

It is very informative for deciphering the genotype of the other individual.

Any allele present in the “non-tester parent” will be expressed in the offspring

Question 15

What are the two probability rules:

Answer 15

(1) The product rule
(2) The sum rule:

Question 16

What is the product rule :

Answer 16

AND rule

The probability of two independent events occurring is the product of the two individual probabilities

Question 17

What is the sum rule:

Answer 17

OR rule

The probability of having one or the other of two mutually exclusive events is the sum of their individual probabilities

Question 18

How are familial relationships and inheritance of traits represented for species that don’t produce very large numbers of offspring from a single mating pair

Answer 18

Pedigree Diagram

Question 18

How are probability and ratios applicable to offspring:

Answer 18

“expected segregation ratios”, such as 3:1, can be recognized in large populations.

However, even in small families, you can think of expected ratios in terms of probabilities
Example: If two individuals of “Bb” genotype mate and have one offspring there is a ¼ chance, (i.e 25%) that the offspring will be “bb” genotype. The frequency of a bb genotype will be 25%.

Question 19

By analyzing pedigree;

Answer 19

We can often decipher the genetic control of a trait

Question 20

In a pedigree, the squares represent:

Answer 20

males

Question 21

In a pedigree, the circles represent:

Answer 21

females

Question 22

In a pedigree, the rows represent:

Answer 22

generations

Question 23

What are the key elements of the pedigree to observe (3):

Answer 23

1) An affected offspring resulting from the mating of two unaffected individuals indicates that this trait is caused by a recessive allele. This also indicates that the parents were both heterozygotes.

2)It is a strong indication, though not proof, that the trait controlled by a dominant allele if all affected individuals in a pedigree have at least one affected parent
3)A high frequency of individuals being affected by a rare trait within a single family also suggests the effect of a dominant allele

Question 24

In a pedigree analysis, we often ask two questions:

Answer 24

(1) Is a trait controlled by a dominant or recessive allele?
(2) What is the probability of a certain individual being affected by a certain genetic trait

Question 25

How can we make inferences and deductions due to the simple logic of genetics (2)?

Answer 25

(1) If we know a trait is controlled by different alleles of a single gene or two genes, we can predict the inheritance of the trait based on probability.
(2) The inverse is also true, if we can recognize a pattern of inheritance for a trait that is like a mendelian ratio 3:1 or 1:, we can conclude that the trait is controlled by a single gene with two alleles

Question 26

What are genes at the molecular level (describe the molecular basis of inheritance)?

Answer 26

The body is made up of cells: each cell has a nucleus that contains chromosomes.

Genes are on chromosomes. They are composed of DNA.

DNA is the template for RNA synthesis.

RNA is translated into proteins.

Proteins regulate the mechanics of the cell

DNA –> RNA –> Proteins –> Development and metabolism

Question 27

Mutations are:

Answer 27

Changes in the DNA sequence that create different alleles of a gene.

Question 28

Mutations often lead to :

Answer 28

non functional proteins

Question 29

The altered metabolism that results from mutations gives:

Answer 29

the varied phenotypes that we see

Question 30

mutations in genes that encode the enzymes that synthesize pigments lead to

Answer 30

different colors found among individuals of a species

Question 31

Altered proteins are the causes of:

Answer 31

Many human genetic diseases

Question 32

The segregation of alleles and random nature of fertilization that mendel obserbed is based on:

Answer 32

The behaviour of chromosomes during meiosis, the cell division that gives rise to gametes

Question 33

In diploid organisms, each cell has two sets of :

Answer 33

homologous chromosomes

Question 34

homologous chromosomes are:

Answer 34

paired chromosomes

Question 35

Humans have __ chromosomes total

Answer 35

46 (22 pairs of autosomal chromosomes and two sex chromosomes)

Question 36

Humans have __ autosomal chromosomes

Answer 36

22 pairs

Question 37

Drosophila melanogaster has:

Answer 37

chromosomes total, 3 pairs of autosomes and 2 sex chromosomes

Question 38

The segregation pattern of chromosomes during meiosis is __

Answer 38

The basis of gene segregation

Question 39

Define Chromosome:

Question 40

Define Chromatid:

Question 41

Define Chromosome Arm

Question 42

Define Centromere

Question 43

Define sister chromatids

Question 44

Define homologous chromosomes, also called homologous pairs of chromosomes:

Question 45

What are the two types of cell division:

Answer 45

Mitosis and meiosis

Question 46

Define mitosis:

Answer 46

cell division that occurs in somatic cells (all cells except those producing gametes).
In mitosis, chromosomes replicate then divide in conjunction with cell division.
This conserves the number of chromosomes during cell division.

Question 47

Define meiosis:

Answer 47

A particular kind of cell division in reproductive cells which give rise to gametes, i.e. egg cells, sperm, and pollen.
In meiosis, chromosome replication is followed by two cell divisions. The number of chromosomes in a gamete is half of the number of chromosomes in a somatic cell because of meiosis. The first cell division separates the members of each chromosome pair from each other; the individual chromosomes maintain their duplicated structures during this first division (meiosis I). The second division (meiosis II) splits each of the duplicated chromosomes into two daughter chromosomes.
The pairing of homologous chromosomes and their segregation into separate gametes accounts for the segregation of alleles of a gene during gametogenesis. The random assortment of genes on different chromosomes accounts for random assortment of genes.

Question 48

How did early geneticists demonstrate that chromosomes carried genetic material?

Answer 48

A. Chromosomes were found to determine sex type

B. Gene inheritance correlated with sex chromosomal inheritance for some traits. These traits are called sex-linked traits

C. Abnormal sex-linked gene inheritance occurred with abnormal sex chromosome inheritance

Question 49

Define and describe sex chromosomes in humans and flies:

Answer 49

Individuals with two X chromosomes are female.

Males have one X and one Y chromosome.

The X and Y chromosomes pair during meiosis and males produce X and Y gametes in equal numbers.

Females produce gametes only with X chromosomes.

Fertilization gives rise to XX and XY offspring

Question 50

Describe sex chromosomes in birds:

Answer 50

The females have heteromorphic sex chromosomes, called Z and W
Males have homomorphic sex chromosomes

Question 51

Sex linkage

Answer 51

Disproportionate inheritance of a trait between male and female offspring usually indicates that a trait is sex-linked.
i.e. a trait is controlled by a gene either on a X or Y chromosome (most often, it is on the X chromosome)

Question 52

Genes on the X chromosome are passed from:

Answer 52

Fathers to daughters
From mothers to either daughters or sons