genetics

Question 1

define locus

Answer 1

position of a gene on a chromosome

Question 2

define allele

Answer 2

alternative form of a gene (each allele has a unique nucleotide sequence, only one of which can occur at a given locus)

Question 3

what is recessive allele

Answer 3

allele that shows its phenotype only in the presence of another identical recessive allele.

in heterozygotes, effect of gene product expressed by recessive allele is masked by effect of gene product expressed by dominant allele

Question 3

What is a dominant allele

Answer 3

allele that shows its phenotype regardless of whether it is homozygous or heterozygous.

in heterozygotes, gene product of dominant allele masks effect of gene product expressed by the other recessive allele.

Question 4

explain codominance

Answer 4

when two different dominant alleles of the same gene are both expressed and influences the phenotype, resulting in a heterozygote phenotype that is different from phenotypes of both homozygotes.

Question 4

explain incomplete dominance

Answer 4

when the phenotype of heterozygotes is intermediate between phenotypes of individuals homozygous for either allele.

Question 5

what is genotype

Answer 5

the combination of alleles, situated on homologous chromosomes at corresponding loci. Genotype determines a specific trait of an organism and are passed to offspring

Question 5

explain a homozygous condition

Answer 5

diploid condition in which alleles at a given locus on a pair of homologous chromosomes are identical

Question 6

explain heterozygous condition

Answer 6

diploid condition in which alleles at a given locus on a pair of homologous chromosomes are different.

Question 7

state 3 environmental factors that affect phenotypic variation

Answer 7

1. Temperature
2. UV light
3. Food/nutrition

Question 7

what is phenotype

Answer 7

characteristic (trait) of an organism that is expressed or observed.

arises from interaction of genotype and environment in which the organisms develops. Environment may alter the appearance of the organism

Question 8

what is linkage

Answer 8

two or more genes on same chromosome that do not assort independently in meiosis and are inherited together.

genes closer together are less likely to cross over and exchange alleles between homologous chromosomes.

Question 9

what is test cross

Answer 9

cross with a homozygous recessive individual

Question 9

briefly describe the law of independent assortment

Answer 9

• homologous pairs of chromosomes align randomly on either side of metaphase plate during metaphase I
• alignment of each homologous pair is independent of other homologous pairs

Question 10

describe monohybrid crosses

Answer 10

are genetic crosses that studies the inheritance of one characteristic controlled by a single gene

Question 11

describe dihybrid inheritance

Answer 11

genetic crosses that studies the inheritance of two different characteristics controlled by two different genes

Question 11

what are linked genes

Answer 11

are located on the same chromosome, usually located physically close enough together on a chromosome that the alleles of the two genes may be inherited together. The closer the gene loci on the same chromosome, the higher the chance that the alleles of the genes will be inherited together as one linkage group

Question 12

what is sex linkage

Answer 12

genes that are carried on the sex chromosomes, that result in a characteristic being expressed mainly in one sex.

1. sons will only obtain these features from their mothers.
2. daughters get their sex-linked features from both parents.

Question 12

features of discontinous variation

Answer 12

1. there are distinct and discrete phenotypes
2. generally caused by different alleles of a single gene
3. their phenotypic expression are usually unaffected by environmental conditions.

Question 13

features of continuous variation

Answer 13

1. differences are slight and phenotypic differences vary along a continuum in graduations, no distinct groupings are formed
2. there is a range of phenotypes for one characteristic
3. usually indicates polygenic inheritance, where multiple genes are involved. There is an additive effect of each gene, where each gene has a small overall effect on a single phenotypic character.
4. polygenic inheritance will result in a bell-shaped normal distribution curve, where intermediate phenotypes are more common than extreme phenotypes
5. phenotypes are affect by environmental factors.

Question 14

define epistasis

Answer 14

a form of gene interaction in which a gene at one locus alters the phenotypic expression of a gene at a second locus

there will be deviation form the 9:3:3:1 ratio in different combinations when two heterozygotes are crossed.

Question 15

what is recessive epistasis

Answer 15

recessive allele of one gene, present in the homozygous condition, masks the phenotypic effects of alleles of the other gene

Question 15

what is dominant epistasis

Answer 15

dominant allele of one gene, present in either homozygous or heterozygous condition, masks the phenotypic effects of alleles of the other gene.