15 genetics Flashcards
what’s a gene
A gene is that part of the DNA molecule
which codes for one polypeptide
what’s an allele
An allele is a particular gene coding for
a specific character
what are the sources of different alleles of a gene
Gene mutations
the changes in the sequence of base pairs in part of a DNA molecule coding for a polypeptide can be one of four types
- Substitution of one or more base pairs by others
- Addition of one or more base pairs
- Deletion of one or more base pairs
- Inversion where a particular nucleotide sequence is reversed
Causes of mutations
They are caused by a number of
chemicals, high energy radiation
e.g. X rays, gamma rays and
ultraviolet light.
what is A mutagen
A mutagen is an agent which
causes a mutation
what are considers Chromosome mutations
include changes in chromosome structure which can happen during division
types of Chromosome mutations
1-duplicated
2-Break off and be lost
3-Break off and rejoin with the sequence of genes inverted
4-Break off and attach to another chromosome
The transfer of a portion of one chromosome to another is called
translocation
what is Chromosome mutations
Changes in chromosome number result from unequal separation of chromosomes between daughter cells during division
what is non-disjunction
After meiosis, one daughter cell may lack one chromosome and the other have one extra chromosome
Chromosomes are present in homologous pairs in
somatic cells
Chromosomes are present in homologous pairs in
somatic cells
There are at least how many alleles for each character
There are at least 2 alleles for each character
A recessive character will only be expressed if
if both alleles are recessive
what does A dominant allele mask
A dominant allele masks the expression of a recessive allele
what does A dominant allele mask
A dominant allele masks the expression of a recessive allele
what is The genotype
The genotype is the genetic constitution expressed in terms of its genes.
what is The phenotype
The phenotype is the observable features that arise from its genetic constitution
what is A monohybrid cross
A monohybrid cross involves a single character that is controlled by one gene with two or more alleles.
Homozygous =
= Pure (Homogeneous)
what is Pure Dominant
the individual only has genes for the dominant trait.
what is Pure Recessive
the individual only has genes for the recessive trait.
Heterozygous =
Mixed (Heterogeneous)
what is A heterozygous
an individual has one dominant gene and one recessive gene for a trait. The result is the dominant gene is the one expressed or shown.
in Autosomal dominant The mutated gene is
a dominant gene and One copy of the gene is
sufficient to have the trait
Autosomal recessive functions
- Two copies of the gene are
necessary to have the trait - Typically not seen in every
generation of an affected family
what is Brachydactyly
its an Autosomal dominant disease and it is a rare condition of humans in which the fingers are very short It is due to a mutation in the gene for finger length tends to occur in members of every generation
what is Albinism
Albinism is a rare inherited condition in which the individual has a block in the biochemical pathway by which the pigment melanin is formed. * Albinos have white hair, very light coloured skin and pink eyes * It shows an autosomal recessive inheritance * It often skips one or more generations altogether
what is Cystic fibrosis
its An autosomal recessive trait that
affects the lungs and digestive system.
The body produces thick and sticky
mucus that can clog the lungs and
obstruct the pancreas.
The red blood cell antigen is coded
for by
by the gene I (for isohaemaglutinogen), which has three alleles IA, IB and IO.
A and IB are codominant, while IO is
recessive.
what is Sickle cell anaemia
- Sickle cell anaemia is a genetic disease in the haemoglobin of the red blood cells
The sickle cell allele causes
haemoglobin to form a long
strands - The red blood cell carrying
these molecules distorts into
a long sickle shape
The shape of the haemoglobin molecule is controlled by two alleles
Normal Haemoglobin allele (HbA)
* Sickle Cell Haemoglobin allele (HbS
)
The genetics of sickle cell anaemia The three phenotype produced are:
- Normal
* Normal individuals have two normal haemoglobin alleles - Sickle cell anaemia
* Sickle cell anaemia patients have two sickle cell alleles in their genotype - Sickle cell trait - 50% of the haemoglobin is affected.
* Sickle cell trait individuals are heterozygotes, having one of each allele
Normal haemoglobin allele is —-
* Sickle cell allele is —-
Normal haemoglobin allele is HbA
* Sickle cell allele is HbS
Genotypes Phenotypes
HbAHbA ———-
HbAHbS ———
HbSHbS ———-
Genotypes Phenotypes
HbAHbA Normal haemoglobin
HbAHbS Sickle cell trait
HbSHbS Sickle cell anaemia
Sex is determined by
by the sex chromosomes (X and Y)
Colorblindness is a recessive and
and X-linked trait (Xb). The allele for normal vision is dominant and is represented by XB
why The presence of many affected individuals in a family does not always mean that the trait is dominant.
because A trait may be recessive but still show up in all generations of a pedigree.
