Mendel’s Law Flashcards
At which stage of meiosis are homologous chromosomes separated?
Anaphase I
How many bivalents can be seen in humans at prophase I of meiosis if 2n = 46?
23 bivalents
Who is considered the founder of genetics?
Mendel
What is Mendel’s principle of Dominance?
One allele can mask the expression of another allele.
What is the phenotypic ratio in a monohybrid cross in the F2 generation?
3:1
What is the phenotypic ratio in a dihybrid cross in the F2 generation?
9:3:3:1
Fill in the blank: Mendel’s first law states that members of a gene pair ______ into gametes equally.
segregate
What does the term ‘pleiotropy’ refer to?
A gene influencing more than one trait.
What is an example of a recessive lethal allele?
Yellow allele in mice.
What is the main cause of Achondroplasia?
A dominant gain-of-function mutation in FGFR3.
True or False: Incomplete dominance results in a phenotype that is a blend of both alleles.
True
What is the definition of ‘penetrance’ in genetics?
The percentage of individuals with a given genotype who exhibit the expected phenotype.
What is ‘variable expressivity’?
The extent to which a genotype is expressed at the phenotypic level.
What is the significance of Alfred Knudson’s two hit hypothesis?
It explains familial cancer syndromes caused by tumor suppressor genes.
What are the three types of point mutations?
- Silent (no effect)
- Nonsense (changes code)
- Missense - either conservative (subtle effect) or nonconserative (causes problem in protein)
What is the relationship between dominance and recessiveness?
Dominance/recessiveness is a relationship between two alleles, not a fixed property.
What does ‘loss of heterozygosity’ mean?
The loss of the healthy allele in a heterozygous individual due to mutation.
Fill in the blank: The universal donor blood type is ______.
O
What is the expected phenotypic ratio of a cross involving a yellow allele that is dominant for coat color?
2:1 due to recessive lethality.
What does co-dominance mean in genetics?
Both alleles in a heterozygote are fully expressed.
What is meant by ‘multiple alleles’?
More than two alleles exist for a gene within a population.
Give an example of a genetic condition affected by pleiotropy.
Primary ciliary dyskinesia (PCD).
What is the impact of gene modifiers on phenotypic expression?
They can affect the expression of a phenotype.
What does Mendel’s First Law state?
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.
What is the key process during Metaphase I in meiosis?
Homologous pairs line up at the equator
This alignment is crucial for the proper segregation of chromosomes.
What is Mendel’s Second Law?
Alleles from different genes segregate randomly into gametes
This law is based on the independent assortment of chromosomes.
Which scientists contributed to the chromosome theory of inheritance?
Walter Sutton and Theodor Boveri
Their work in the early 1900s established parallels between Mendel’s laws and chromosome behavior.
What did Thomas Hunt Morgan use to demonstrate that genes are located at specific regions of chromosomes?
Fruit fly
Morgan’s work earned him a Nobel Prize in 1933.
What occurs during Meiosis II?
Segregation of sister chromatids
This process ensures that each gamete receives only one chromatid from each chromosome.
In the context of Mendel’s laws, what is the significance of equal probability in gamete formation?
Each type of gamete is produced with equal probability
This is essential for the genetic variation seen in offspring.
Fill in the blank: Mendel’s First Law derives from the segregation of _______ in Meiosis I.
homologous chromosomes
This segregation leads to the formation of equal numbers of different types of gametes.
True or False: Mendel’s Second Law is a consequence of the random alignment of pairs of homologous chromosomes.
True
This alignment occurs during Metaphase I of meiosis.
What is produced at equal frequency in the gametes according to Mendel’s Second Law?
Each possible combination of alleles
This reflects the independent assortment of alleles from different genes.
What is the principle of independent assortment?
Only works if genes are on different chromosomes or very far apart
What is Mendel’s theory of inheritance?
- 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
What is the effect of a nonsense mutation?
Causes truncated form
Null allele = no activity from that protein
(Loss of function)
What is the effect of a missense mutation?
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
What are the general rules of mutations?
- LOF alleles are mostly recessive
- GOF alleles are mostly dominant
What is incomplete dominance?
Heterozygote phenotype is intermediate between the 2 homozygote phenotypes
What is co-dominance?
Heterozygote shows phenotype of both alleles
What is a lethal allele?
Can cause skewed phenotypic ratios
What is an example of incomplete penetrance?
Breast cancer susceptibility
What does Mendel’s first law derive from?
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
What is Mendel’s second law a consequence of?
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)
