Midtrimester Flashcards
What is the law of segregation ?
The two alleles for each gene separate during gamete formation.
The two alleles of each gene pair must segregate, that is, separate, into different gamete cells during the formation of eggs and sperm in the parents.
In which ratio is a dominant trait presented?
3:1 ratio over the recessive trait in the F2 generation.
How is it called a different version of the same gene?
allele
What is the difference between genotype and phenotype?
The alleles found in an individual are called its genotype. An individual’s genotype has a profound effect on its phenotype.
What will be the offspring of individuals of pure breeding?
Heterozygous, with an individual with the dominant phenotype.
What will happen with an heterozygote cross?
genotype ratio of 1:2:1
Phenotype of 3:1
Ratio of a dihybrid cross of nonlinked genes
Ratio phenotype 9:3:3:1
Genotype: R-Y-, R-yy, rrY-, rryy
Law of independent assortment
Alleles of genes on non homologous chromosomes assort independently during gamete formation.
The phenotype of a homozygote is the same as the phenotype of the heterozygote
Complete dominance
AA=Aa
Incomplete dominance
snapdragons, 1:2:1 ratio and they present an intermediate phenotype (Aa)
Co-dominance
Both alleles can be seen in the heterozygote
Pleiotropy
When a gene has several phenotypic effects.
Epistasis
a gene at one locus alters the phenotypic expression of a gene at a second locus.
in Labrador retrievers and many other mammals, coat colour depends on two genes
quantitative characters
are those that vary in the population along a continuum.
What does quantitative inheritance usually means ?
That there is polygenic inheritance. Polygenic inheritance h
Such as height or skin color, that is influenced by two or more genes. Because multiple genes are involved, polygenic traits do not follow the patterns of Mendelian inheritance
Multifactorial
phenotype of a character depends on environment as well as genotype
Test cross
Cross of a F1 with a recessive parental
Backcross
Cross of a hybrid F1 with parent
Monohybrid cross
Organisms that are heterozygous at one gene locus
Dihybrid
An organism who is heterozygous at two gene loci AaBb
How can the ratio in genes change?
Linked genes (on same chromosomes) – different ratios
Incomplete dominance – more classes
Epistasis (gene interaction) – less classes
Lethal types – less classes or reduced number
What are some autosomal diseases?
Albinism
Cystic fibrosis
sickle cell
What needs to happen for X- linked recessive to be expressed?
*Female needs to have two copies of the allele (homozygous recessive)
*A male only need to have one copy of the gene.
X- linked recessive diseases
red-green colour blindness, Duchenne muscular dystrophy and haemophilia
Dominantly inherited disorders
Some human disorders are caused by dominant alleles. Dominant alleles that cause a lethal disease are rare and arise by mutation At least one parent of the affected individual is affected.
X inactivation
one of the two X chromosomes in each cell is randomly inactivated early in embryonic development. The inactive X condenses into an object called a Barr body.
Which kind of genes do not assort independently ?
Linked genes do not assort independently as they are both in the same chromosome
What happens with linked genes that have a recombinant frequency of nearly 50%?
Genes that are far apart on the same chromosome can have a recombination frequency near 50%. Such genes are physically linked, but genetically unlinked, and behave as if found on different chromosomes.
abnormal number of chromosome/s
Aneuploidy
= more than 2 complete chromosome sets eg, triploidy (3n), tetraploidy
Polyploidy
more than 2 of a particular chromosome in diploid cells
Polysomy
Klinefelter syndrome is the result of an extra X chromosome in a male, producing XXY individuals. Results in a male phenotype, sometimes with certain female body characteristics.
only one of a particular chromosome in diploid cells
Monosomy
Monosomy X, called Turner syndrome, produces XO females, who are sterile and may have other characteristic features
three copies of a particular chromosome in diploid cells
Trisomy
Down syndrome
results from three copies of chromosome 21.
Occurs when a chromosomal fragment is lost. The affected chromosome is then missing certain genes. (If the centromere is deleted, usually the entire chromosome will be lost.)
Deletion
The syndrome cri du chat (“cry of the cat”), results from a specific deletion in chromosome 5 ie. del 5p
A child born with this syndrome is mentally retarded and has a catlike cry; individuals usually die in infancy or early childhood.
: The “deleted” fragment may become attached as an extra segment to a sister chromatid, producing a duplication. Alternatively, a detached fragment could attach to a nonsister chromatid of a homologous chromosome
Duplication
A chromosomal fragment may also reattach to the original chromosome but in the reverse orientation
Inversion
Moves a segment of a chromosome to another
Translocation
Philadelphia chromosome
Translocation chr 922 is associated with chronic myelogenous leukemia
What does hydroxyurea does?
Hydroxyurea blocks ribonucleotide reductase, the rate-limiting enzyme responsible for converting ribonucleotides to deoxyribonucleotide triphosphates (dNTPs). Deoxyribonucleotide triphosphates are needed for DNA synthesis.
