Genes Flashcards
What is heredity?
The study of inheritance.
What is population genetics?
the study of the gene pool organism over time.
What are molecular genetics?
The study of the molecular structure and function of genes.
What is a gene and how is it defined?
What about to a molecular geneticist?
A gene is an inherited factor that affects the characteristics of an individual.
It is defined by the affect on the phenotype of the organism.
It is also part of a chromosome involved in the transcription of DNA into RNA.
What is a wild type?
Functional
What is a loss of function?
non functional. usually recessive.
What is a gain of function?
A new or enhanced function. Usually dominant.
What is the difference between a wild type and a mutant?
wild type & loss of function = wild type.
wild type and gain of function = mutant.
What is an exon?
Code for proteins, they express sequences.
Part of DNA that is converted into mRNA.
What is an intron?
Do not code for proteins. They intervene sequences.
Present in the inital RNA transcript, and must be removed for the mRNA to do its job.
What happens if a LOF allele is dominant?
Haploinsufficiency.
Describe mitosis.
Somatic cells, producing two genetically identical daughter cells.
2 x 2n
Describe meiosis.
produces 4 haploid daughter cells.
4 x n
Describe interphase.
All the cells DNA is replicated, each chromosome consists of two identical sister chromatids joined at the centromere.
Cell now has four copies of each chromosome as opposed to two.
Describe the stages of meiosis.
PMAT I & II
What is a bivalent?
A homologous pair of chromosomes, each consisting of two sister chromatids, paired for meiosis.
Compare meiosis and mitosis. No of divisions Products Chromosome no Bivalents formed Crossing over occurring
Mitosis. Meiosis
No of divisions:
One. Two
Products:
Two identical Four different
daughter cells
Chromosome no:
Maintained. Halved
Bivalents:
No. Yes
Crossing over:
No. Yes
What is the locus?
The position of a gene on a chromosome.
What is crossing over?
When lengths of DNA are swapped from one chromatid to another.
What are the consequences of meiosis?
Gametes are haploid (somatic cells are diploid).
Genetically
different from each other because …
•chromosome orientation at Metaphase I is random
•crossing-over shuffles segments of homologous
chromosomes
How does meiosis lead to genetic variation?
Crossing over shuffles alleles.
Genetic reassignment due to the random distribution of maternal and paternal chromosomes during meiosis I.
Genetic reassortment due to the random distribution and segregation of the sister chromatids at meiosis II.
Random mutation.
Describe how crossing over occurs.
Prophase I.
The homologous chromosomes pair and come together to form Bivalents.
Non sister chromatids wrap around each other very tightly and attach at the chiasmata.
The chromosomes may break at these points, which then rejoin to ends of the chromatids in the same bivalent.
The sections that swap contain the same genes but different alleles.
Produces new combinations of alleles on the chromatids.
Where do chromatids join during crossing over?
At the chiasmata.
Describe how the reassortment of chromosomes occurs.
In metaphase I there is a random distribution of chromosomes on the spindle equator.
Each gamete acquires a different mixture of maternal and paternal chromosomes.
Describe how the reassortment of chromatids occurs.
Happens in metaphase II.
The chromatids are randomly distributed on the spindle equator.
Because of crossing over the sister chromatids are not identical.
Learn mitosis cycle.
notes.
How are sister chromatids joined?
By sister chromatic cohesion.
When are homologous chromsomes seperated?
anaphase I
How many bivalents can be seen at prophase I of meiosis in humans?
3 bivalents each with 4 chromatids. In P1 2n=6.
What is Mendels first law?
Principle
of Segregation: Alleles of a single gene segregate randomly
and equally into gametes
What is the freq of the dominant B allele in a population of 100 with the genotypes: 30 BB, 60 Bb, 10 bb,
0.6 since (30 x 2) + 60 = 120
120=200
What is the ratio for a monohybrid cross?
RR x rr
3:1 in the F2 generation.
All dominant in F1.
What is the ratio for a dihybrid cross?
RR yy x rr YY
9:3:3:1 in F2.
What is Mendel’s second law?
Principle of independent assortment. Alleles from different genes segregate randomly into gametes.
Why are the four offspring of meisis different?
Independent assortment of maternal/paternal chromosomes.
Crossing over.
What is Mendel’s theory of inheritence?
•Characters are distinct, and hereditary
determinants (genes) are particulate in nature
•Each adult has two genes for each character-different forms of the genes are called alleles
•Members of the gene pair segregate equally into
gametes, so that each gamete has only one of the
two genes (Mendel’s first law)
•Fusion of the gametes at fertilisation restores the
pair of genes and is random
•Different genes assort independently in gametes
(Mendel’s second law)
What is incomplete dominance?
Heterozygotes show an intermediate phenotype.
Ratio 1:2:1
What is co dominance?
Heterozygotes show phenotype of both alleles.
Blood cells.
Describe multiple alleles.
There may be more than two alleles for a gene.
What is Pleiotropy?
When a gene may influence more than one trait.
ie. Sickle cell haem give resistance to malaria.
Heterozygote HbA Hbs have highest fitness.
Describe lethal alleles.
Can cause skewed phenotypic ratios.
Describe Achondroplasia.
homozygous for it causes death. heterozygote results in a dwarf. neither parent affected, arises from a new mutation.
What does a 9:3:3:1 ratio indicate?
2 genes involved - 4 phenotypes.
What is epistasis?
The interaction between two or more genes that control a single phenotype.
Usually one gene masks the phenotypic effect of another.
What is the recessive epistatic ratio?
9:4:3
Why is the albino c allele epistatic to all other coat colour genes?
the albino allele is a recessive loss of function mutation in the enzyme Tyrosinase which is required for the synthesis of melanin pigments in melanocytes.
What is the dominant epistatic ratio?
12:3:1
What is proliferation?
Division.
Why is the dominant white W allele epistatic to other coat colour genes?
dominant white is a dominant loss-of-function mutation in a transmembrane growth factor receptor required for proliferation (division) and migration of melanocytes