Genetics Flashcards
mitosis and meiosis were discovered when?
1875 and 1890s
Mendel’s factors during sexual life cycles
- Chromosomes are present in diploid cells
- Homologous chromosomes segregate during meiosis
- Fertilization restores paired diploid condition
According to chromosome theory of inheritance
- Mendelian genes have specific loci on chromosomes
-Chromosomes undergo segregation and independent assortment
Fruit fly experimentation
- the wild type allele was dominant
-concluded that the eye colour gene must be located on the x-chromosome
Humans have _____ pairs of chromosomes
23
Of the 23 pairs of chromosomes 22 are _____
Homologous/autosome
(same size and contain the same genes)
The 23rd pair of chromosomes are considered _____ and is called the _______
not a true pair
sex chromosomes
Two varieties of the 23rd chromosome
X and Y
(XX = female)
(XY = male)
The x-0 system
What creatures use this system?
22 + XX = female
22 + X = male
grasshoppers, crickets, and cockroaches, as well as some arachnids and nematodes
The Z-W system
What creatures use this system?
76 + ZW = female
76 + ZZ = male
birds, some reptiles (like snakes and lizards), some insects (like butterflies and moths), and some fish and crustaceans
The haplo-diploid system
What creatures use this system?
16 (diploid) = female
16 (haploid) = male
Hymenoptera (bees, ants, and wasps) and Thysanoptera (thrips), as well as sporadically in some spider mites, Hemiptera, Coleoptera (bark beetles), and rotifers
When a female ovulates, the egg released contains
an x-chromosome
22 autosomes
When sperm is produced it contains
22 autosomes
an x or a y chromosome
What determines the sex of a child
the chromosome that the sperm carries
Drosophila eye colour gene is an illustration of the principle…
genes that are located on the sex chromosomes do not necessarily have to do with sexual function
Genes on human sex chromosomes that are completely unrelated to sexual function are called?
-sex linked genes
Sex linked genes are commonly referred to as?
Because?
x-linked
in human terms the x-chromosome contains more important genes
X-linked genes in humans follow the same pattern of inheritance that Morgan observed for the eye-colour locus in Drosophila, such as…
- generally males pass their x-chromosome to their daughters but not their sons
-females pass 1 of 2 of their chromosomes to 1/2 daughter + sons
Holandric genes
any gene located on the y chromosome
X-linked dominant patterns
things that are always true:
a) affected males pass to all daughters, none of the sons.
b) affected females pass to at least 1/2 daughters and 1/2 sons
How do X-linked genes and Holandric genes differ?
- Holandric genes are much smaller and contains fewer genes
- Holandric genes also have no x-counterpart and encode for traits only found in males
(father to son)
X inactivation in females
- prevents females from receiving a double dose of sex linked genes by inactivating one of the x chromosomes forming a dense dark object called Barr bodies
Cells of females and males have the same ______ of genes on the _______–
effective dose
x-chromosomes
The choice of which an X chromosomes inactivates occurs ______ and _______ in every cell
randomly
independently
inactivation and the tortoise shell cat
the tortoise shell genes is on the ______
and the phenotype requires the presence of __________
x chromosome
two different alleles, one for orange fur one for black fur
in tortoise shell cats
Normally only _____ can have both alleles because they have ______
females
two x chromosomes
In tortoise shell cats if a female is heterozygous for the tortoise shell gene she is
tortoise shell
Mosaicism
a condition where an individual possesses two or more distinct cell populations with different genetic makeup, arising from a single fertilized egg due to postzygotic mutation
In humans, mosaicism can be seen in
A heterozygous woman has
anhidrotic ecodermal dysplasia ( a skin disorder )
patches of normal skin and patches of skin lacking sweat glands
Genetics is the study of
heredity - how traits are passed from parents to offspring
The particulate theory of heredity was put forth by?
In what year?
Gregor Mendel
1860’s
Gregor Mendel’s theory of heredity
parents transmit physical factors (now called genes) to their offspring, which retain their identity in the offspring
Another name for Gregor Mendel
the father of genetics
In 1857 Mendel breed what…?
garden peas in the monastery abbey garden to study inheritance
Why did Mendel choose garden peas as a model organism had several advantages
-Seven distinct varieties (seed shape, seed colour, pod colour, flower position, and stem length)
-Characters varied in an “either or” manner (either purple flowers or white or either tall or short. no in between)
-He could strictly control which plants mated with which
-Easy and cheap grow
True breeding
when cells always produce the same variety
Law of Segregation
The two factors separate when the gametes are formed, and only one factor is present in each gamete
Gene
A section of a chromosome that codes for a trait
Locus
The position on a chromosome where a specific gene is located
Allele
Two or more alternative versions of gene. They vary in nucleotide sequence
Genotype
An organisms specific genetic composition; many times referring to a single gene
Homozygous
An organism that has a pair of identical alleles for a gene
Heterozygous
An organism that has two different alleles for a gene
Phenotype
An organism’s expressed traits
When is the multiplication rule used?
to calculate the probability of two independent events occurring together
When is the addition rule is used?
When any one of two or more mutually exclusive events will occur together is calculated by adding together their individual probabilities
Pleotropic Gene
a single gene that has multiple phenotypic effects
example of pleiotropic gene
albinism ( pale skin, hair and eyes)
Epistasis
where a gene at one locus alters the phenotype produced by a gene at a second locus
Polygenic Inheritance
where two or more genes control a phenotype
skin colour in human is controlled by how many genes
3
phenotype for a character depends on _________ as well as on genotype
the environment
phenotype plasticity
capacity to develop traits suited to the environment experienced by an organism by varying patterns of gene expression
