Genetic Variation (I)

Question 1

def. Homologous chromosomes

Answer 1

Homologous chromosomes have the same genes that determine a certain trait at corresponding loci.

Question 2

def. Locus

Answer 2

Position of a gene on a chromosome.

Question 3

def. Gene

Answer 3

An ordered sequence of DNA nucleotides located at a particular locus on a chromosome. It encodes a specific functional product.

Question 4

def. Allele

Answer 4

Alternative form of a gene. Each allele has a unique nucleotide sequence, only one of which can occur at a given locus.

Question 5

def. Homozygous

Answer 5

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

Question 6

def. Heterozygous

Answer 6

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

Question 7

def. Genotype

Answer 7

Combination of alleles, situated on homologous chromosomes at corresponding loci. Genotype determines a specific trait of an organism and are passes to offsping.

Question 8

def. Phenotype

Answer 8

Characteristic of an organism that is expressed or observed.

Question 9

Incomplete dominance

Answer 9

In Incomplete dominance, the heterozygote exhibits a phenotype that is intermediate between the two homozygous forms.

Question 10

Codominance

Answer 10

In codominance, both alleles of the gene are equally expressed in the phenotype of a heterozygote.

Question 11

def. Lethal alleles

Answer 11

Lethal alleles causes death if the organism is homozygous for that allele.

Question 12

def. Sex linkage

Answer 12

Sex linkage refers to genes that are carried on the sex chromosomes that result in a characteristic being expressed mainly in one sex.

Question 13

def. Multiple alleles

Answer 13

Multiple alleles is a condition where a single characteristic appears in several different forms as it is controlled by 3 or more alleles, of which any two may occupy the same locus on homologous chromosomes.

Question 14

Gregor Mendel’s Law of Segregation

Answer 14

Gregor Mendel’s Law of Segregation states that the two alleles for each trait separates during the formation of gametes. This ensures a parent with two copies of each gene can pass on either allele.

Question 15

Test cross

Answer 15

A test cross is designed to reveal the genotype of an organism that exhibits dominant traits. A test cross is carried out by crossing with an individual expressing homozygous recessive trait.

Question 16

Mendel’s Law of Independent Assortment

Answer 16

Mendel’s Law of Independent Assortment states that alleles of different genes on different pairs of chromosomes assort independently of each other. This is because:

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

Question 17

Pedigree

Answer 17

A pedigree is a diagram of family relationships that uses symbols to represents people and lines to represent genetic relationships.

Question 18

Reciprocal cross

Answer 18

A reciprocal cross is used to determine if a particular characteristic is sex-linked. In a reciprocal cross, 2 separate crosses are conducted using the same characteristic, but the sexes are reversed.

• Phenotypic frequencies of reciprocal crosses will be different if the characteristic is sex-linked.
• If the characteristic is not sex-linked, the results of the reciprocal cross will be the same.