week 8 Flashcards
early hypothesis for inheritance
pangenesis
who was the father of modern genetics and what was he known for?
gregor mendel
- a priest who studied physics and mathematics
- studied pea plants in 1856 and published the results ten years later
- work was ignored then discovered in 1900
why did he study peas?
they have advantages in their properties
- many Dif varieties with different characteristics
- easy to produce true breeding lines
- normally are self fertilizing
- flowers are easy to manipulate and use for crosses
single factor crosses
a cross that follows the variants of only one character
what are the generations of a single factor cross?
p generation
f1 generation
f2 generation
f1 gen
first gen offspring of a p cross (called monohybrids in single-factor crosses)
f2 gen
f1 monohybrids self-fertilize to produce the f2 generations
key takeaways from menders data
no blending
traits were “hidden” in the f1 generation but reappeared in the f2 generation
in the f2 ben 3/4 plants showed f1 trait while 1/4 showed hidden trait
(3:1 ratio)!!!!
three important ideas in patterns of inheritance
- traits may exist in two forms dominant and recessive
- an individual carries low genes for a character, and genes have variant forms called alleles!
- the 2 alleles of a gens separate during the process that gives rise to haploid cells and gametes, so each sperm and egg receives only one allele
mendels law of segregation of alleles
two copies of a gene segregation from each other during gametes formation, so every gamete recieves only one allele (Tt > T and t)
genotype
genetic composition of individual
homozygous
individuals with to identical copies of a gene
heterozygous
individuals with two different alleles of the same gene
Punnett squares
A common way to predict the outcome of Simple genetic crosses
· Example: What offspring are expected in a cross between heterozygous tall plants?
genotypic ratio
TT, Tt and tt in a 1:2:1 ratio
phenotypic ratio
tall and dwarf in a 3:1 ratio
testcross
To distinguish between the homozygous dominate and heterozygous genotypes, a testcross can be used
· An individual with a dominate phenotype is crossed to a homozygous recessive individual
· Phenotypes of offspring are examined
· Presence of recessive trait indicates parent was heterozygous
two factor crosses
Follows the inheritance of two different characters
· We can imagine tow hypothesis for what might happen
Two genes would segregate together and always be inherited together
- Linked assortment
- Predicts a 3:1 ratio of phenotypes
Two genes are independent, so their alleles are randomly distributed into the gametes
- Independent assortment
- Predicts a 9:3:3:1 ratio
menders law of independent assortment
the alleles of different genes assort independently of each other during the process that gives rise to gametes (as long as they are far apart or on different chromosomes)
what does the chromosome theory of inheritance state and who proposed it?
Theodor boveri and Walter Sutton, showed that the inheritance pattern of traits could be explained by chromosome behavior during meiosis
first fundamental principle of inheritance
chromosomes contain DNA which is the genetic material (genes are found in the chromosomes
second fundamental principle of inheritance
chromosomes are replicated and passed from parent to offspring, and from cell to cell during multicellular development
third fundamental principle
The nucleus of a diploid cell contains two sets of chromosomes, which are found as homologous pairs
a. One member of each pair is inherited from the mother and the other from the father. Each set carries a full complement of genes
fourth fundamental
At meiosis, one member of each chromosome pair segregates into one daughter nucleus and its homologue segregates into the other daughter nucleus
a. During the formation of haploid cells, the members of different chromosome pairs segregate independently
fifth fundamental law
Gametes are haploid cells that combine to form a diploid cell during fertilization, which each gamete transmitting one set of chromosomes to the offspring
locus
physical location of a gene on a chromosome
chromosomal basis of allele segregation (3 points)
- Chromosomes replicate, and cell progresses to metaphase of meiosis I
- Homologous segregate into separate cells during meiosis I
- Sister chromatids separate during meiosis II to produce 4 haploid cells \ (Diploid cell (Tt) turns into 4 haploid cells (2 with t’s and 2 with T’s
chromosomal basis of independent assortment (3 Points)
- Chromosomes replicate, and cell progresses to metaphase of meiosis I. Alignment of homologous can occur in more than one way
- Homologous segregate into separate cells during meiosis I
- Sister chromatids separate during meiosis II to produce 4 haploid cells (Heterozygous diploid cell (YyRr) to undergo meiosis à 4 haploid cells (yR, yR, Yr, Yr)
what is pedigree analysis?
Examines the presence of the trait over course of a few generations in one family
· Used to understand the inheritance of generic diseases that follow simple Mendelian patterns
o Disease symptoms can occur as a result of a mutant allele
o A pedigree helps determine whether the mutant allele is dominate or recessive
o Allows for prediction of the likelihood of an individual being affected
human disease: recessive or dominant?
Many human genetic diseases are recessive
o Disease alleles persist in heterozygote carries who are not affected
§ Due to a “lack” in dominate which does not form correctly
o Unaffected parent have affected children
o Pedigree will show parents with a heterozygote gene passing the gene down and a person will only be affected if 2 heterozygote genes mix with one another
· Huntington Disease is an example of a human genetic disease that is dominate
o Symptoms appear later in life, usually after reproduction
§ Produces a “toxic” protein who causes symptoms to occur and causes disease to present
§ Caused by a defective, abnormal protein
o Normal allele encodes a protein that functions in nerve cells
o Mutation encodes an anormal form of the protein, which aggregates in cells and results in defective nerve function
o Pedigree would show effected people at every generation because every effected person will have an effected parent
autosome
pairs of chromosomes found in both sexes
sex chromosomes
distinctive pair of chromosomes that differs between males and females
human chromosomes
46 total (22 pairs of autosomes = 44 + one pair of sex chromosomes)
males are XY and females are XX
x-linked traits
Sex Linked genes are found on one sex chromosome but not on the other
o In humans, the X chromosome is larger and carries more genes than the Y chromosome
o Genes found on X chromosome but not the Y are known as X-linked genes
· Males are hemizygous for X-linked genes
o Have only one copy of each X-linked gene
o Disease caused by recessive X-linked mutant allele occur more frequently in males
