Genetic Crosses

Question 1

What are gametes?

Answer 1

Haploid cells that are capable of fusing with each other. They are formed by meiosis.

Question 2

Define fertilisation.

Answer 2

The joining of a haploid male gamete with a haploid female gamete to form a diploid zygote.

Question 3

What are somatic cells?

Answer 3

Non-sex cells (not gametes)

Question 4

What are alleles?

Answer 4

Different variants of a gene

Question 5

What is a locus?

Answer 5

The place where a certain gene is positioned on a chromosome

Question 6

Define autosomes.

Answer 6

Non-sex chromosomes

Question 7

What are sex chromosomes?

Answer 7

The X and Y chromosomes

Question 8

What gene does the Y chromosome contain that determines sex?

Answer 8

The SRY gene

Question 9

True or False: The Y chromosome carries sex-linked conditions.

Answer 9

False

Question 10

What is a dominant allele?

Answer 10

An allele that will be expressed even in the presence of a recessive allele

Question 11

Define a recessive allele.

Answer 11

An allele that is not expressed in the presence of a dominant allele

Question 12

What does genotype refer to?

Answer 12

Genetic make-up, i.e. the set of gene variants the organism has

Question 13

What is phenotype?

Answer 13

Physical make-up, i.e. the set of physical traits that are expressed in the organism

Question 14

What is progeny?

Answer 14

What offspring are produced during a genetic cross

Question 15

Define homozygous.

Answer 15

Having two copies of the same allele

Question 16

What does heterozygous mean?

Answer 16

Having two different alleles of a gene

Question 17

What is incomplete dominance?

Answer 17

The expression of alleles is not masked leading to an intermediate phenotype

Question 18

Who is Gregor Mendel?

Answer 18

Father of genetics. He bred garden peas to show how genetic crosses work.

Question 19

What is the Law of Segregation?

Answer 19

Inherited characteristics are controlled by pairs of alleles that separate during gamete formation.

Question 20

Define the Law of Independent Assortment.

Answer 20

When gametes are formed, either member of a pair of alleles is equally likely to join with either member of another pair of alleles.

Question 21

What does linkage refer to in genetics?

Answer 21

Genes are located on the same chromosome

Question 22

What are sex-linked genes?

Answer 22

Genes located on the sex chromosomes

Question 23

Provide examples of sex-linked diseases.

Answer 23

• Haemophilia
• Colour blindness

Question 24

What types of plants did Gregor Mendel use in his experiments?

Answer 24

Tall and short plants, round and wrinkled seeds

These traits were used to study inheritance patterns.

Question 25

What was the result of crossing a pure tall plant with a pure short plant?

Answer 25

All offspring were pure tall ## Footnote This demonstrated that the tall trait is dominant.

Question 26

What was the outcome of crossing a plant that produced smooth seeds with a plant that produced wrinkled seeds?

Answer 26

All offspring were smooth ## Footnote This indicates that the smooth seed trait is dominant.

Question 27

What was the ratio of smooth to wrinkled seeds in the second generation offspring?

Answer 27

3:1 ratio ## Footnote This ratio applies to all traits in the second generation offspring.

Question 28

Fill in the blank: All traits had a _______ ratio in the 2nd generation offspring.

Answer 28

3:1

Question 29

What does the term 'dominant gene' refer to in Mendel's experiments?

Answer 29

A gene that masks the presence of another gene ## Footnote In Mendel's case, the tall plant and smooth seed traits were dominant.

Question 30

What method did Mendel use to produce the second generation of plants?

Answer 30

Self-fertilization ## Footnote This allowed him to observe the inheritance patterns of traits.