Inheritance (3.4, 10.2)

Question 1

What concepts did Gregor Mendel discover and how did he discover these?

Answer 1

The law of allele segregation, the principle of dominance and independent assortment. He discovered these concepts by performing experiments on pea plants.

Question 2

Phenotype

Answer 2

A structure, process, behaviour or feature of an organism that is determined by its genotype. Observable characteristics.

Question 3

Genotype

Answer 3

An organism’s genetic makeup.

Question 4

Heterozygous

Answer 4

Two different alleles eg. Tt

Question 5

Homozygous

Answer 5

Identical copies of the allele eg. TT or tt

Question 6

1st filial

Answer 6

The heterozygous (Tt) offspring of a cross between two purebred parents (eg. TT and tt).

Question 7

2nd filial

Answer 7

The offspring of a cross between two 1st filial offspring.

Question 8

What is a Punnett square?

Answer 8

A predicted ratio for all possible allele combinations for potential offspring of one gene.

Question 9

What is a test cross used for?

Answer 9

To tell if the dominant phenotype is homozygous (eg. TT) or heterozygous (eg. Tt). A plant w the dominant phenotype is mated with a homozygous recessive plant.

Question 10

How is a dihybrid test cross carried out?

Answer 10

An unknown genotype is mated with a known homozygous recessive. If the unknown parent is homozygous dominant (AABB) all offspring will express the dominant phenotype. If the unknown parent is heterozygous (AaBb) half the offspring should be dominant and half recessive.

Question 11

What is incomplete dominance?

Answer 11

When one allele is not completely dominant over the other. The heterozygote is a mixture of the two alleles eg. a pink flower formed by a red flower crossed with a white flower.

Question 12

What is co-dominance?

Answer 12

When both alleles are independently and equally expressed in the heterozygote. Eg. a mixture of red and white hairs NOT pink hair

Question 13

Define the term lethal alleles

Answer 13

Lethal alleles are gene mutations that result in a gene product that is non functional and affects the organisms survival.

Question 14

What are the human ABO blood grouping genotypes?

Answer 14

A = IAIA or IAiB = IBIB or IBiAB = IAIBO = ii

Question 15

What does homogametic mean?

Answer 15

Two similar sex chromosomes. Eg. Females are XX

Question 16

What does heterogametic mean?

Answer 16

Two unlike sex chromosomes. Eg. Males are XY

Question 17

What is sex determination based on?

Answer 17

The presence or absence of the Y chromosome.

Question 18

Why are most sex-linked conditions usually X-linked?

Answer 18

The Y chromosome is much shorter than the X chromosome. Therefore it has no corresponding gene to a faulty gene on the X, so cannot mask the effect.

Question 19

Who are the carriers for X-linked conditions?

Answer 19

Females, as they can be heterozygous carriers.

Question 20

Define sex linkage

Answer 20

When a gene controlling a characteristic is located on a sex chromosome (can be X or Y).

Question 21

What are linked genes?

Answer 21

Groups of genes that are on the same chromosome and move together during meiosis (i.e. don’t independently assort).

Question 22

Why are linked gene-phenotype ratios different to non-linked gene-phenotype ratios?

Answer 22

Because the phenotype ratio for linked genes will be closer to a monohybrid cross as the two genes are inherited as a single unit.

Question 23

What is the effect of crossing over on linked genes?

Answer 23

Crossing over occurs in Prophase I of Meiosis. Homologous pairs of sister chromatids undergo synapsis where they line up side by side. During synapsis, the chromatids may tangle (chiasmata formation) and exchange pieces of DNA (this is coined crossing over). If linked genes become separated by a chiasma an exchange of alleles will occur between non-sister chromatids causing the formation of new allele combinations different to those of the parents.

Question 24

What is the purpose of a Chi-squared table?

Answer 24

To determine whether the difference between an observed and expected frequency distribution is statistically significant.

Question 25

Define polygenic traits

Answer 25

Characteristics controlled by two or more genes.