Inheritance Flashcards
What is a Genome?
complete set of chromosomes of an organism. usually a copy of each cell
What is an allele?
A variant nucleotide sequence for a particular gene at a given locus which codes for a different phenotype, same gene - different types
What is the locus?
specific location of a gene on a chromosome
What is a gene?
sequence of DNA which codes for a protein
What is a genotype?
All the alleles an individual has
What does homozygous mean?
both alleles are the same for a particular gene from both parents
What does heterozygous mean?
different alleles for a particular gene from each parent
what is a phenotype?
visible characteristics, gene/allele that codes for the outward expression of a genotype in a specific environment
what does dominant mean (genetics)?
allele always expressed when present
What does recessive mean (genetics)?
allele only expressed when homozygous, not expressed in presence of dominant allele
What are the properties of continuous variation?
Is a measurement, has a scale
What are the properties of discontinuous variation?
is categorical
What are some examples of continuous variation?
height, weight etc.
What are some examples of discontinuous variation?
Hair colour, blood type etc.
How can continuous variation be represented?
on a line graph
How can discontinuous variation be represented?
Bar graph
What is continuous variation controlled by?
lots of genes and environment - range of phenotypes between 2 extremes, like height in humans
what is discontinuous variation controlled by?
a few genes - limited number of phenotypes with no intermediates. like A, B, AB, O blood groups in humans
If both parents are heterozygous for brown eyes (Bb) what would the offspring look like?
25% homozygous brown (BB), 50% heterozygous brown (Bb). 25% homozygous blue (bb)
How could you check to see if an organism is heterozygous or homozygous for a dominant characteristic?
test cross/ back cross
What is test crossing? + results?
crossing of an unknown individual representing dominant trait with individual representing recessive phenotype. If any of the offspring express the recessive trait then the dominant parent must be a heterozygous dominant allele.
What is co-dominance?
in heterozygous - some cells express dominant allele other cells express recessive allele e.g. holstein friesian cattle (black and white patched cows)
What is incomplete dominance?
in heterozygous - intermediate between the recessive and dominant allele e.g. Palamino horses (linked with chestnut (brown) and cremello (white) horses)
What is monohybrid inheritance?
the inheritance of the alleles of a single gene, 2 different alleles, dominant one represents characteristic
What is a genetic diagram?
shows how characteristics are inherited, phenotype and genotype of parents, gametes, and ratio of offspring
What does F1 mean?
First Filial Generation (filial is the offspring of a cross)
What is dihybrid inheritance?
simultaneous inheritance of 2 unlinked genes
What did Mendel explore to do with dihybrid inheritance?
relationship of peas, as to whether they were round or wrinkled, yellow or green
What ratios did Mendel discover between round(R) yellow(Y) wrinkled(r) and green(y)?
RY:Ry:rY:ry 9:3:3:1
What is Mendel’s law of segregation?
the characteristics of an organism are determined by factors (alelles) which occur in pairs, only one of the pair is present in each gamete.
Each member of a pair of alleles may combine randomly with either of a another pair on a different chromosome
What is Mendel’s law of independent assortment?
the alleles of two (or more) different genes get sorted into gametes independently of one another
segregation of alleles for one gene into different gametes is independent to any other gene
What is Mendel’s law of dominance?
recessive alleles will be masked by dominant alleles (not so for co-dominance or incomplete dominance
What is independent assortment?
Genes which are unliked can combine with any alleles in gametes. genes for different traits are inherited independently of each other. e.g. eye colour and eye shape
What is a dihybrid test cross?
test for genotype of parent for 2 different features by crossing with recessive organism for both features (it will outwardly express this characteristic)
What is the purpose of the Chi-sqaured test?
test for statistical difference in the numbers of offspring expressing specific characteristics
What is the null hypothesis?
‘there is no significant difference between the observed and expected values’
What is a pedigree diagram?
‘family trees’ way of graphically illustrating inheritance patterns over a number of generations (commonly used to study inheritance of genetic disorders)
what is linkage?
genes on same chromosome are inherited together
what can crossing over do?
may separate genes and produce new combination of alleles (it is rare)
What is the parental genotype?
no crossing over, only copy of one parents genotype, alleles on the chromosome.
What is the recombinant genotype?
only happens if crossing over occurs, contains alleles from both parents, is a new genotype
What are angiosperms? what is there determination of sex?
flowering plants, they are hermaphrodites so have both sexual organs
How do plants prevent self fertilisation?
stigma is hidden or less accessible by chance, stigma and anthers mature at different times
What are some examples of lower phylum hermaphrodites?
garden snail
worms
What is sexual dimorphism?
a distinct difference in size or appearance between sexes in addition to sexual organs themselves
How is human sex determined?
by chromosomes
XX and XY
What is sequential hermaphroditism?
limpets in pile, fertilise the female at bottom of chain, they move away, then next limpet becomes female to be fertilised
How is sex determined within bees?
by their ploidy level
unfertilised eggs are haploid and become male drones
fertilised eggs are diploid and become female workers
How is sex determined in turtles?
temperature of eggs can turn on and off genes for sex
How is siamese cat affected by temperature?
if in colder place the extremeties will have gene for melanin turned on, so will result in black paws, tail, ears and face. if it is warmer it will be turned off and result in more white cat.
How is sex determined in clown fish?
Dominant Female and Dominant Male supress breeding of others in the group. If dominant female dies or leaves, dominant male with take over this place. becoming a female.
eggs produce male or female offspring
What gene controls inheritance of Y chromosome?
SRY gene
What is klinefelter syndrome?
1/500 males are XXY 1/18000 males are XXYY
What can happen to Y chromosome in men? why?
they can lose Y chromosome with increasing age
other factors that increase it:
smoking
alcohol consumption
SRY gene on Y chromosome codes for what?
everything male, (testes male genitalia in embryo
What can a mutation in SRY lead to in XY genotype?
female genitalia despite XY genotype
What is the difference between X chromosome on males and females regarding inheritance?
alleles on X chromosome in female can either be dominant or recessive depending on expression
alleles on X chromosome in males will be expressed regardless of dominance
What is haemophilia?
An inherited disorder in which the blood does not clot due to insufficient clotting factors
What chromosome is haemophilia carried on?
X
What represents a normal allele in haemophilia?
X^H
What represents a mutated allele in haemophilia?
X^h
How many possible genotypes are there in males? what are they? for haemophilia
2
X^HY
X^hY
What does the genotype X^HY mean?
Male with blood that clots normally
What does the genotype X^h mean?
Male with haemophilia
How many different genotypes are the of haemophilia in females? what are they?
3
X^HX^H
X^HX^h
X^hX^h
What does the genotype X^HX^H mean?
homozygous dominant blood clots normally
What does the genotype X^HX^h mean?
heterozygous blood clots normally, this person is a carrier of haemophilia (but is not affected)
What does genotype X^hX^h mean?
homozygous recessive, person has haemophilia
Is haemophilia more prevalent in males or females? why?
males
as only needs one mutant allele to be affected
What are is Duchenne Muscular Dystrophy (DMD)?
An inherited disorder characterised by progressive muscular weakness
What are the affects on a child with DMD ages 5-7 years?
motor delay
enlarged calves
toe walking
standing from supine, climbing stairs more difficult
What are the affects on a child with DMD ages 8-11 years?
increasing loss of walking ability
part time wheelchair use
What are the affects on early teens with DMD?
loss of ambulation
full-time wheelchair use
increasing loss of upper limb function
What are the affects on teens with DMD?
increasing respiratory impairment
ventilation support often required
unable to perform activities of daily living
What are the affects of DMD on teens to twenties?
increasing cardiac dysfunction
heart failure
death
How is DMD inherited compared with haemophilia?
in the same way
What 3 things are gene expression influenced by?
physiological effects of the environment
differences in DNA nucleotide sequences
Epigenetic modifications
Give 2 examples of a physiological effect of the environment and what it affects?
light intensity affects plant growth
temperature dependent albinos - melanin produced when cold from enzyme tyrosenase e.g. Siamese cat, can give extremities black fur like ears, face, paws
What is an epigenetic modification?
environment altering expression of genes by affecting how they are transcribed, without changing sequence
How do epigenetics work?
they are heritable changes in the gene function
do not change DNA sequence
What are the 2 types of epigenetics?
Post-replication methylation
Histone modification
What is DNA methylation?
the addition of methyl groups to DNA sequence
What happens if there are many methyl groups on a DNA strand?
there will be less transcription
Application: If tumour suppressor gene was heavily methylated what would happen?
It would be less likely to be transcribed, less proteins coding for tumour suppressor gene, leading to a higher chance of tumour growth
What are histones?
proteins that provide structural support for a chromosome
where are histones found?
nucleus
What are the functions of histones?
Histones bind to DNA, help give chromosomes their shape, help control the activity of genes
What are some examples of histone modification?
acetyl group to lysine
methyl group to lysine to argnine
In Histone modification what does unmodified mean?
nucleosomes pack tightly = transcription reduced
In Histone modification what does modified mean?
nucleosomes uncoil = transcription increased
