Transmission Genetics

Question 1

Describe transmission genetics

Answer 1

How traits/genes are passed from parent to offspring

Question 2

Define true-breeding/pure-breeding strains

Answer 2

Homozygous organisms that when self-fertilized or intercrossed produce offspring with the same phenotype

ex. PP (purple flowers), pp (white flowers)

Question 3

Define reciprocal crosses and give an example to clarify

Answer 3

A cross between two different parental phenotypes and a second cross in which the sexes are switched

ex.
cross 1: female with purple flowers (PP) x male with white flowers (pp)
cross 2: female with white flowers (pp) x male with purple flowers (PP)

Question 4

Define test crosses

Answer 4

crossing an individual with a dominant phenotype but an unknown genotype with a second dominant recessive individual

Question 5

Define dominant phenotype

Answer 5

The phenotype that is expressed in a heterozygous organism

This would be the same phenotype expressed as in a dominant homozygote

Question 6

Define recessive phenotype

Answer 6

The phenotype that would only be expressed if an individual was homozygous recessive

Ie., the recessive phenotype is not expressed in a heterozygous individual

Question 7

Define homozygous genotype

Answer 7

When both the alleles in a diploid genotype are the same

Question 8

Define heterozygous genotype

Answer 8

When the alleles in a diploid genotype are different

Question 9

Define dominant allele

Answer 9

The allele that will be expressed in the phenotype of an individual that is heterozygous or homozygous dominant

Question 10

Define recessive allele

Answer 10

The allele that will only be expressed in the phenotype if an individual is homozygous recessive

Question 11

Define phenotypic ratio

Give an example

Answer 11

The ratio of offspring that express each phenotype

ex. offspring from a monohybrid cross will have the ratio 3:1
ex. offspring from a dihybrid cross will have the ratio 9:3:3:1

Question 12

Define genotypic ratio. Give an example

Answer 12

The ratio of offspring that have each genotype

ex. 1/4 heterozygous: 1/2 homozygous: 1/4 heterozygous in a monohybrid cross

Question 13

Define a monohybrid cross

Answer 13

A genetic cross between individuals that are heterozygous for ONE gene

Question 14

Describe a monohybrid cross in terms of genotypes and phenotypes (parental, F1, F2) and gametes (parental, F1)

Answer 14

The parental individuals will be true-breeding (ex. GG x gg)

100% of the F1 offspring will express the dominant phenotype and have the heterozygous genotype (ex. Gg)

the monohybrid cross is when the F1 generation is crossed (ex. Gg x Gg)

The F2 generation will result in a 3:1 phenotypic ratio and a 1/4 heterozygous: 1/2 homozygous: 1/4 heterozygous genotype

Gametes:

one parent will give a G and one parent will give a g

The F1 will have GG, Gg, gg, gG

Question 15

Explain Mendel’s Law of Segregation referencing chromosome behaviour during meiosis

Answer 15

Ensures that each of the 4 gametes produced by meiosis will only receive one type of allele of each gene

Question 16

Describe the general structure of a eukaryotic chromosome

Answer 16

Chromosomes are condensed chromatin fibres wrapped tightly around specific proteins

Chromatin/chromosomes are very long and thin fibres of DNA and proteins

Question 17

Describe a gene

Answer 17

A linear sequence of hundreds-thousands of DNA nucleotides located on a chromosome

Genes carry the information cells need to make proteins that express different hereditary traits

Question 18

Explain the relationship between genes, chromosomes, and DNA

Answer 18

A gene is composed of many DNA nucleotides and is located on a chromosome

Question 19

Define sister chromatids

Answer 19

During S phase, a single chromosome will copy itself and form a second identical chromosome and they will combine with their genes aligned to form a sister chromatid

Question 20

Define homologous pairs

Answer 20

During prophase I of meiosis, 2 sets of sister chromatids that have the alleles for the same genes will join via synapsis at their centromeres to form homologous pairs

2 sets of sister chromatids joined - one sister chromatid will have one allele of a gene and the second sister chromatid pair will have the other allele for the same gene

Question 21

Describe the cell cycle

Answer 21

a cycle of events that occur in order from the formation of a new cell to the division of that cell into new cells

Question 22

Describe mitosis and state it’s functions

Answer 22

a type of cell division that occurs in diploid or haploid somatic (body) cells and generates 2 new identical cells

functions:

• asexual reproduction
• growth
• cell replacement

Question 23

Describe meiosis and state its functions

Answer 23

a type of cell division that occurs only in diploid gametes (sex cells) and generates four genetically unique haploid cells

functions in sexual reproduction and is responsible for genetic diversity

Question 24

Why does the S phase of interphase precede mitosis and meiosis I but not meiosis II?

Answer 24

S phase is necessary to begin cell division because individual chromosomes must be duplicated in order for there to be enough genetic information for cells to divide into new functioning cells

Not necessary for meiosis II because there is already enough chromosomes to do a division a second time

Question 25

Describe the steps of meiosis I

Answer 25

G1: chromatins condense into chromosomes

S: chromosomes duplicate and form sister chromatids

prophase I: sister chromatids form homologous pairs

metaphase I: homologous pairs align randomly along the metaphase plate

anaphase I: homologous pairs are pulled apart to the opposite poles

telophase I & cytokinesis: cytoplasm divides and 2 cells form with different sister chromatids

Question 26

Describe the steps of meiosis II

Answer 26

In each of the two cells:

Sister chromatids align randomly on the metaphase plate in metaphase II

Sister chromatids are pulled apart to either pole in anaphase II

The two cells divide into two each (total 4) in telophase II and cytokinesis

Question 27

Describe independent assortment

Answer 27

Independent assortment during metaphase I is when the homologous pairs align along the metaphase plate independently from one another

Question 28

Describe segregation

Answer 28

Segregation of homologous pairs occurs during anaphase I of meiosis when they are pulled from the metaphase plate into either pole. This will ensure that only one allele of each gene is distributed into each gamete.

Question 29

Define synapsis

Answer 29

the pairing of two sister chromatids to form a homologous pair during prophase I

Question 30

What is the purpose of synapsis?

Answer 30

to allow for crossing over

Question 31

When does crossing over happen?

Answer 31

prophase I

Question 32

Define synaptonemal complex / what is the purpose of this?

Answer 32

protein structure that forms between homologous chromosomes during prophase I

allows for chromosome pairing, synapsis and crossing over

Question 33

describe crossing over

Answer 33

during prophase I, sister chromatids join by synapsis to form homologous pairs and can exchange genetic material with each other

Question 34

Describe chiasmata

Answer 34

the location where homologous pairs are attached