inheritance and variation Flashcards
alleles?
varieties of a gene
crossing over of TT and tt
f1 progeny-all Tt
T
t
dominant
recessive
homozygous
same gene, eg: TT, tt
heterozygous
different, eg: Tt
monohybrid cross
A monohybrid cross is a genetic mix between two individuals who have homozygous genotypes
segregation
separation of alleles of the parental pair from each other and only one allele is transmitted to a gamete
test cross
it’s an experiment in which the dominant phenotype with an unknown genotype is crossed with a recessive parent
LAWS OF INHERITANCE
- law of dominance
2. law of segregation
law of dominance
Mendel’s law of dominance states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic
law of segregation
refer to def. of segregation
incomplete dominance
when the dominant trait is not completely expressed when the recessive trait (allele) is around,eg: snapdragon flower
codominance
were both the traits or alleles are expressed in the f1 progeny eg; determine ABO blood grouping in humans
ABO controlled by -
GENE I
multiple alleles
Multiple alleles exist in a population when there are many variations of a gene present
explain starch synthesis on the basis of gene
- its controlled by one gene , it has 2 alleles B and b
- its properly synthesized by BB homo zygotes and produce larger amounts
- bb homozygotes have lesser efficiency in starch synthesis
- in Bb seeds starch is produced in intermediate amounts
- BB seed are round , bb are wrinkled
dihybrid cross
a cross between 2 pairs of alleles ,eg:HhSs and hhss
law of independent assortment
it states that the segregation of one pair of character is independent of the other pair of character ( alleles are not linked )
why was mendels work not excepted?
due to
- lack of communication
- non blending inheritance
- use of mathematics to explain biology
- no physical proof of the existence of genes and chromosomes
who are the 2 scientists who rediscovered mendele’s work
de vries , correns and von teschermak
boveri - sutton theory ?
its now called the chromosomal theory of inheritance , it sates that individual genes are found at specific locations on the chromosome , the pattern of behaviour of chromosomes during meiosis explains the mendel
laws as to why , how genes are created
expalin the work of thomas hunt morgan
he worked with tiny fruit flies , drosophila melanogaster
they were suitable because they could be grown in a synthetic medium in a lab , the male and the female flies could be differentiated , they complete their life cycle in 2 weeks , can produce large no. pf progeny flies
polygenic traits
when many genes code for one trait , eg; skin colour , height
pleiotropic gene
where one gene exhibits multiple phenotypic expressions
disease phenylketonuria?
it occurs in humans which is caused by the mutation in the gene which codes for the enzyme phenyl alanine hydroxylase. this manifests itself through phenotypic expressions which result in mental retardations , hair loss and pale skin
autosome
An autosome is any chromosome that is not a sex chromosome
number of chromosomes in human male and female
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair, the sex chromosomes, differ between males and females
X0 type of sex determination
Males only have one X chromosome (X0), while females have two (XX). O signifies the lack of a second X. Maternal gametes always contain an X chromosome, so the sex of the animals’ offspring depends on whether a sex chromosome is present in the male gamete.
example of xo type
grasshoppers
Do you think the number of chromosomes in male and female are equal in grasshopper?
NO
male heterogamety
The production by males of some species, such as humans and Drosophila, grasshopper, of two types of gametes that differ in their sex chromosome content.
female heterogamety
2 different types of gametes in terms of sex chromosome are produced by females like in birds
sex determination in honey bee
haploid diploid system
female honey bee-
male -
develop from a fertilized egg
develop from an unfertilized egg by parthenogenesis
parthenogenesis
is a natural form of asexual reproduction in which the growth and development of embryos occur without fertilization by sperm.
female honey bee-
male …-
diplod(36)
haploid(16)
mutation
it’s a phenomenon that results in the alteration of DNA sequence which results in the change of phenotype and genotype of the organism
how mutation occurs?
by loss or gain of DNA result in change in chromosomes, exposure to ionizing radiation, exposure to chemicals called mutagens
point mutation?
when there’s is a change in a single base pair of DNA
eg; sickle cell anemia
deletion and insertion of base-pair result in frame-shift mutation
pedigree analysis
By analyzing a pedigree, we can determine genotypes, identify phenotypes, and predict how a trait will be passed on in the future. The information from a pedigree makes it possible to determine how certain alleles are inherited: whether they are dominant, recessive, autosomal, or sex-linked.
Mendelian disorders
they are determined by a mutation in a single gene
Mendelian disorders examples
Sickle cell anaemia. Cystic fibrosis. Thalassemia. Phenylketonuria. Colour blindness. Haemophilia.
Colour blindness.
it is a sex-linked recessive disorder, carried on the x chromosome, due to defect in either green or red cone of the eye resulting in failure to differentiate between red and green colour which is due to mutation of certain genes in the X chromosome
haemophilia
sex-linked recessive trait, here a single protein that is a part of the cascade of proteins which is involved in the clotting factors is affected so a single cut will result in non-stop bleeding
sickle cell anaemia
it is an autosome linked recessive trait
it is caused when both the parents are carriers for the gene, it is controlled by the allele HBA and HBS, the individual should be homozygous(HBS HBS)to show the disease
what is HBA and HBS
HBA - Normal haemoglobin
HBS- sickle haemoglobin
how sickle cell anaemia is caused
it is caused by the substitution of glutamic acid by valine at the 6th position of the beta-globin chain
phenylketonuria
autosomal recessive trait, here the person lacks the enzyme that coverts phenylalanine into tyrosine as a result phenylalanine levels increases and the tyrosine decreases as result phenylalanine is converted to phenyl pyruvic acid. accumulations of these in the brain result in mental retardation
thalassemia
autosomal recessive trait
2 types depending upon which chain of the haemoglobin is affected (alpha and beta-globin)
beta-thalassemia
where there’s a deficiency in the production of the beta-globin chains of the haemoglobin, here it is controlled by a single gene HBB on the 11 chromosome of each parent and occurs due to mutation of one or both the genes
alpha thalassemia
where there’s a deficiency in the production of the alpha-globin chains of the haemoglobin, it is controlled by 2 linked genes HBA1 and HBA2 on chromosome 16
of the 2 parents and it’s observed due to mutation or deletion of one or more of the 4 genes
chromosomal disorders
it is caused by the excess or abnormal or absence of arrangement of one or more chromosomes
aneuploidy
causes when there’s a failure in the segregation of the chromatids during cell division which results in excess or loss of chromosomes
polyploidy
causes when there’s a failure in the cytokinesis after telp\ophase stage during cell division which results in an increase in a whole set of chromosomes in an organism which often occurs in plants
trisomy
gain of an additional copy of a chromosome
monosomy
loss of any one pair of chromosome
down syndrome
down syndrome is a condition in which a child is born with an extra copy of their 21st chromosome — hence its other name, trisomy 21. This causes physical and mental developmental delays and disabilities.
turners syndrome
absence of one of the X chromosome, 45 with X0
results in lack of secondary sexual characters
klinefelters syndrome
Klinefelter syndrome is a genetic condition affecting males due to a presence of an additional copy of chromosome resulting in karyotype 47
symptoms of Klinefelter’s syndrome
they have overall masculine characters but also some feminine development like breasts
