Genetics

Question 1

What is a monohybrid cross?

Answer 1

A cross between two purebreeding lines each with different alleles for the character being studied (e.g. a cross between AA and aa). 100% of the offspring is heterozygous

Question 2

What genotypic ratios are produced when the offspring of a monohybrid cross are crossed with themselves?

Answer 2

3:1 (Aa x Aa = 3 Aa and 1 aa)

Question 3

Define: wildtype

Answer 3

The phenotype of the typical form of a species as it occurs in nature (the normal, non-mutated form)

Question 4

What is a dihybrid cross?

Answer 4

A cross between two purebreeding lines each with two unrelated characters. 100% of the offspring is heterozygous. (E.g. AABB x aabb = 100% AaBb)

Question 5

What genotypic ratios are produced when the offspring of a dihybrid cross are crossed with themselves?

Answer 5

9:3:3:1 (AB, Ab, aB, aa)

Question 6

What is a testcross?

Answer 6

A cross between a homozygous recessive individual and an unknown individual

Question 7

What is a backcross?

Answer 7

A cross between the F1 progeny and either of thier purebreeding parents.

Question 8

Define: Epistasis

Answer 8

The interaction of genes that leads to the suppression of one such gene by another.

Question 9

What is co-dominance?

Answer 9

When the alleles of two phenotypes are equally recognisable in the individual

Question 10

What is incomplete dominance?

Answer 10

When an organism is heterozygous but does not display the phenotype of the dominant allele, rather an intermediate of the dominant and recessive genotypes

Question 11

Describe X chromosome inactivation

Answer 11

Females carry double the amount of gene rich X chromosomes and so one is inactivated and condenses into a Barr body

Question 12

Examples of the effect of environment on phenotypes

Answer 12

Siamese cats (lower body temp at extremeties causes darker fur), hydrangeas ( alkaline soil = pink, acid soil = blue)

Question 13

What is hemizygous?

Answer 13

A gamete with only one gene present; either the result of a gene deletion or the chromosome is heterogametic (XY)

Question 14

What is an autosome?

Answer 14

A non-sexual chromosome (e.g. in humans, not X and Y)

Question 15

Turner’s syndrome

Answer 15

Affects female, absence of an X chromosome (XO), sterile, webbed neck skin

Question 16

Klinefelter’s syndrome

Answer 16

Affects males, extra X chromosome (XXY), sterile

Question 17

Triple X

Answer 17

Affects females (XXX), fertile

Question 18

Double Y

Answer 18

Affects males (XYY), claimed to be aggressive

Question 19

What is the SRY

Answer 19

The Sex Determining Region is a locus on the Y chromosome which determines maleness if present. (I.e. XX = female). Complete absence on the Y chromosome causes sterility.

Question 20

What is Mendel’s Law of Independant Assortment?

Answer 20

Allele pairs separate independently during the formation of gametes. This means that traits are transmitted to offspring independently of one another. (E.g. double hetero x double homo recessive = 1:1:1:1)

Question 21

When is Mendel’s Law of Independent Assortment not upheld?

Answer 21

If two genes in question are found on the same chromosome, crossing over creates new combinations (via recombination).

Question 22

The frequency of crossing over is affected by?

Answer 22

Distance betweent the loci (the closer they are, the less likely they are to cross over)

Question 23

Map Distance

Answer 23

= (no. of recombinant progeny / total no. of progeny) x 100

Question 24

What are the 5 conditions of HWE

Answer 24

1) Random mating 2) large population 3) no gene flow 4) no mutation 5) no natural selection

Question 25

Anisogamy

Answer 25

Large gametes (more robust), small gametes (higher frequency) therefore 2 populations will form (e.g. the Moa and kiwi)