Mendel’s Law

Question 1

At which stage of meiosis are homologous chromosomes separated?

Answer 1

Anaphase I

Question 2

How many bivalents can be seen in humans at prophase I of meiosis if 2n = 46?

Answer 2

23 bivalents

Question 3

Who is considered the founder of genetics?

Answer 3

Mendel

Question 4

What is Mendel’s principle of Dominance?

Answer 4

One allele can mask the expression of another allele.

Question 5

What is the phenotypic ratio in a monohybrid cross in the F2 generation?

Answer 5

3:1

Question 6

What is the phenotypic ratio in a dihybrid cross in the F2 generation?

Answer 6

9:3:3:1

Question 7

Fill in the blank: Mendel’s first law states that members of a gene pair ______ into gametes equally.

Answer 7

segregate

Question 8

What does the term ‘pleiotropy’ refer to?

Answer 8

A gene influencing more than one trait.

Question 9

What is an example of a recessive lethal allele?

Answer 9

Yellow allele in mice.

Question 10

What is the main cause of Achondroplasia?

Answer 10

A dominant gain-of-function mutation in FGFR3.

Question 11

True or False: Incomplete dominance results in a phenotype that is a blend of both alleles.

Answer 11

True

Question 12

What is the definition of ‘penetrance’ in genetics?

Answer 12

The percentage of individuals with a given genotype who exhibit the expected phenotype.

Question 13

What is ‘variable expressivity’?

Answer 13

The extent to which a genotype is expressed at the phenotypic level.

Question 14

What is the significance of Alfred Knudson’s two hit hypothesis?

Answer 14

It explains familial cancer syndromes caused by tumor suppressor genes.

Question 15

What are the three types of point mutations?

Answer 15

• Silent (no effect)
• Nonsense (changes code)
• Missense - either conservative (subtle effect) or nonconserative (causes problem in protein)

Question 16

What is the relationship between dominance and recessiveness?

Answer 16

Dominance/recessiveness is a relationship between two alleles, not a fixed property.

Question 17

What does ‘loss of heterozygosity’ mean?

Answer 17

The loss of the healthy allele in a heterozygous individual due to mutation.

Question 18

Fill in the blank: The universal donor blood type is ______.

Answer 18

O

Question 19

What is the expected phenotypic ratio of a cross involving a yellow allele that is dominant for coat color?

Answer 19

2:1 due to recessive lethality.

Question 20

What does co-dominance mean in genetics?

Answer 20

Both alleles in a heterozygote are fully expressed.

Question 21

What is meant by ‘multiple alleles’?

Answer 21

More than two alleles exist for a gene within a population.

Question 22

Give an example of a genetic condition affected by pleiotropy.

Answer 22

Primary ciliary dyskinesia (PCD).

Question 23

What is the impact of gene modifiers on phenotypic expression?

Answer 23

They can affect the expression of a phenotype.

Question 24

What does Mendel’s First Law state?

Answer 24

Alleles of a single gene segregate randomly and equally into gametes

This law explains how each gamete inherits only one of the two alleles with equal probability.

Question 25

What is the key process during Metaphase I in meiosis?

Answer 25

Homologous pairs line up at the equator ## Footnote This alignment is crucial for the proper segregation of chromosomes.

Question 26

What is Mendel's Second Law?

Answer 26

Alleles from different genes segregate randomly into gametes ## Footnote This law is based on the independent assortment of chromosomes.

Question 27

Which scientists contributed to the chromosome theory of inheritance?

Answer 27

Walter Sutton and Theodor Boveri ## Footnote Their work in the early 1900s established parallels between Mendel’s laws and chromosome behavior.

Question 28

What did Thomas Hunt Morgan use to demonstrate that genes are located at specific regions of chromosomes?

Answer 28

Fruit fly ## Footnote Morgan’s work earned him a Nobel Prize in 1933.

Question 29

What occurs during Meiosis II?

Answer 29

Segregation of sister chromatids ## Footnote This process ensures that each gamete receives only one chromatid from each chromosome.

Question 30

In the context of Mendel's laws, what is the significance of equal probability in gamete formation?

Answer 30

Each type of gamete is produced with equal probability ## Footnote This is essential for the genetic variation seen in offspring.

Question 31

Fill in the blank: Mendel's First Law derives from the segregation of _______ in Meiosis I.

Answer 31

homologous chromosomes ## Footnote This segregation leads to the formation of equal numbers of different types of gametes.

Question 32

True or False: Mendel’s Second Law is a consequence of the random alignment of pairs of homologous chromosomes.

Answer 32

True ## Footnote This alignment occurs during Metaphase I of meiosis.

Question 33

What is produced at equal frequency in the gametes according to Mendel’s Second Law?

Answer 33

Each possible combination of alleles ## Footnote This reflects the independent assortment of alleles from different genes.

Question 34

What is the principle of independent assortment?

Answer 34

Only works if genes are on different chromosomes or very far apart

Question 35

What is Mendel’s theory of inheritance?

Answer 35

- characters are distinct and hereditary determinants (genes) are particular in nature - each adult has 2 genes (from mother and father) for each character = alleles - members of the gene pair segregate equally into gametes (meiosis) so that the gamete is haploid - fusion of gametes at fertilisation restores diploidy - different genes assort independently in gametes

Question 36

What is the effect of a nonsense mutation?

Answer 36

Causes truncated form Null allele = no activity from that protein (Loss of function)

Question 37

What is the effect of a missense mutation?

Answer 37

Conservative - slight effect on function of enzyme, no effect on phenotype but may have slightly reduced activity = loss or gain of function Nonconservative - causes loss or gain (always active) of function

Question 38

What are the general rules of mutations?

Answer 38

- LOF alleles are mostly recessive - GOF alleles are mostly dominant

Question 39

What is incomplete dominance?

Answer 39

Heterozygote phenotype is intermediate between the 2 homozygote phenotypes

Question 40

What is co-dominance?

Answer 40

Heterozygote shows phenotype of both alleles

Question 41

What is a lethal allele?

Answer 41

Can cause skewed phenotypic ratios

Question 42

What is an example of incomplete penetrance?

Answer 42

Breast cancer susceptibility

Question 43

What does Mendel’s first law derive from?

Answer 43

Law of segregation Segregation of homologous chromosomes in meiosis I and the segregation of sister chromatids in meiosis II so that equal numbers of gametes of each type are formed in a heterozygote

Question 44

What is Mendel’s second law a consequence of?

Answer 44

Independent assortment Random alignment of pair of homologous chromosomes (bivalents) at the cell equator in metaphase I of meiosis (only applies to genes on different chromosomes)