inheritance Flashcards
gene
can separate and combine, mutate and code for the production of specific polypeptides
homozygous
If both alleles of a gene are the same they are homozygous e.g. TT, tt.
chromosome
formed by a single molecule of DNA and exist in homologous pairs to hold the genetic code in form of genes
what is an allosome
sex determining chromosome NOT AUTOSOME!!!!!!!
locus
position of a gene on a chromosome
alleles
alternative forms of genes
dominant
Of the pair of alleles in a monohybrid cross, the one that always produces an effect on the phenotype of the organism when present is the dominant allele.
recessive
The allele that produces an effect on the phenotype only when present as an identical pair is the recessive allele
co-dominant
phenotype
The appearance of an organism – it is determined by the genotype.
variation
differences between individuals of the same species, caused by genes, environment or both
discontinuous variation
clear-cut differences in a characteristic e.g. tall and dwarf pea plants.
what is discontinuous variation caused by?
one of more forms of a single gene - alleles
continuous variation
no clear groups- characteristics form a range of values e.g. height.
what is continuous variation caused by?
several genes acting together - polygenic
what can homozygous individuals called?
pure breeding - does not tell you if it is dominant or recessive.
what is monohybrid inheritance?
a single characteristic controlled by one gene
what is the law of segregation
the characteristics of an organism are determined by alleles which occur in pairs. only one of a pair of factors can be present in a single gamete
what is the ratio in F2 in codominant alleles?
1:2:1
what blood groups are co-dominant?
A and B
what blood group is recessive?
O is recessive (to A and B)
what is dihybrid inheritance?
the inheritance of two characteristics coded for by two separate genes
what is linkage of genes?
any two genes that occur on the same chromosome are usually inherited together.
what is a linkage group?
all the genes on the same chromosome
what happens to linked genes during cell division?
linked genes remain together (NOT following Mendel’s 2nd law of independent assortment)
how is sex determined?
by a pair of chromosomes. Other chromosomes are called autosomes
In humans, which sex chromosomes are homologous and non-homologous?
female - homologous (XX)
male - non-homologous (XY)
What is the ratio for male to female gametes?
1:1
What are the differences between the X and Y chromosome?
The X chromosome is very small and contains very few genes, but the X chromosome is large and contains thousands of genes for important proteins
What kind of proteins are found in the X chromosome?
- Rhodopsin - a light absorbing pigment found in the membrane of retina photoreceptor cells
- blood clotting proteins
- muscle proteins
Which chromosome are recessive alleles carried?
The X chromosome
How is the haemophiliac (recessive) allele carried?
- Male can’t pass on the allele to his sons as they receive the Y chromosome.
- All daughters receive the recessive allele so will be carriers. They have a 50% chance of passing the condition to their offspring
What is Haemophilia caused by?
- caused by a recessive allele on X chromosome
- gene codes for factor VIII a protein involved in blood clotting
why is haemophilia so dangerous?
potentially lethal condition-inability of blood to clot leads to slow persistent bleeding
How can haemophiliacs lead near normal lives?
It is possible to extract Factor from donated blood
What is Duchenne muscular dystrophy (DMD)?
a progressive loss of strength by muscle degeneration
what is the cause of DMD?
- recessive allele on X chromosome
- a mutation in the gene that codes for dystrophin
What is the issue if dystrophin is absent in DMD?
absent muscle cells are easily damaged. progressive muscle weakness leads to serious medical problems with issues relating to the heart and lungs
What is the lifespan of those with DMD?
Young men with Duchenne typically live into their late 20s
