Genetics SAC 1B

Question 1

Diploid

Answer 1

Cells with two sets of chromosomes (2n), one set derived from each parent. In humans the diploid number is 46

Question 2

haploid

Answer 2

Cells with one set of chromosomes (n). These cells are produced by meiosis. In humans the haploid number is 23

Question 3

Gene

Answer 3

A section of DNA that codes for a protein, basic unit of heredity.

Question 4

Allele

Answer 4

Alternative form of a gene

Question 5

Genotype

Answer 5

genetic makeup of an individual, wither in relation to a trait, or a set of traits. e.g. FF, Ff, ff

Question 6

Phenotype

Answer 6

The physical, biochemical, physiological expression of the genotype. It is influenced by the environment

Question 7

recessive

Answer 7

2 identical alleles must be present to observe the trait

Question 8

autosomal

Answer 8

gene is located on an autosome

Question 9

sex-linked

Answer 9

gene is located on the sex chromosome

Question 10

heterozygous

Answer 10

2 different alleles. e.g, Ff

Question 11

homozygous

Answer 11

2 identical alleles. e.g. FF or ff

Question 12

complete dominance (dominant trait)

Answer 12

one allele completely masks the effect on another allele. Dominant traits are observed if only one copy of the affected allele is present.

Question 13

co dominance

Answer 13

both alleles are expressed in a heterozygous therefore a third phenotype is observed.

Question 14

multiple alleles

Answer 14

where there are more than two alleles for a particular gene in the population, but only 2 can ever be present in an individual. E.g. blood groups

Question 15

continuous variation

Answer 15

many intermediate forms of the trait, which follow a normal distribution. E.g. height in humans

Question 16

discontinuous variation

Answer 16

descrete, non-overlapping classes of phenotypes.

Question 17

monogenic inheritance

Answer 17

trait determined by one gene with two or more alleles.

Question 18

polygenic inheritance

Answer 18

trait determined by many genes.

Question 19

Pedigree

Answer 19

graphic representation using standard symbols showing the pattern of occurrence of an inherited trait in a family.

Question 20

Monohybrid crosses

Answer 20

a cross in which alleles of only one gene are involved.

Question 21

Test cross

Answer 21

a mating (set up by humans) where an individual with the dominant phenotype is crossed/ mated with an individual with the recessive trait.

Question 22

Why are test crosses used?

Answer 22

they can determine whether the parent with the dominant trait is homozygous or heterozygous, by observing the ratio of dominant to recessive traits in the offspring.