Heredity Unit 5 Flashcards
Genetics
the study of heredity and heredity variation
heredity
the transmission of traits from one generation to the next
asexual vs sexual reproduction
asexual:
- single individual
- no fusion of gametes
- clones: offspring are exact copies of parent
- through mitosis
sexual:
- two parents
- offspring are unique combination of genes from parents
- genetically varied from parents and siblings
Homologous chromosomes
a pair of chromosomes that carry the same genetic information
_____ have DNA that is packaged in chromosomes
eukaryote
what are autosomes
chromosomes that do not determine sex (humans have 22 pairs)
fertilization
when a sperm cell (haploid) fuses an egg. (haploid) to form a zygote (diploid)
meiosis
a process that creates haploid gamete cells in sexual reproducing diploid organisms
- results in daughter cells with half the number of chromosomes as the parent cell
mitosis vs meiosis
mitosis:
-somatic cells, 1 division, results in 2 diploid daughter cells, daughter cells are genetically identically
meiosis:
forms gametes, 2 divisions, results in 4 haploid daughter cells, each daughter cell is genetically unique
prophase I
- synapsis: homologous chromosomes pair up and connect to each other to form a tetrad.
- crossing over: occurs at the chiasmata and DNA is exchanged between homologous chromosomes.
metaphase I
Independent orientation: tetrads line up at the metaphase plate
anaphase I
homologous pairs separate
-sister chromatids are still attached
telophase and cytokinesis I
- nuclei and cytoplasm divide
- now a haploid set of chromosomes in each daughter cell
prophase II
-spindle forms
metaphase II
- chromosomes line up at the metaphase plate
- chromatids are unique
anaphase II
sister chromatids separate and move to opposite poles
telophase and cytokinesis II
- 4 haploid cells
- nuclei will reappear
- each daughter cell is genetically unique
genotype
the genetic makeup (alleles) for an organism
phenotype
an organisms appearance which is determined by a genotype
testcrosses help
determine whether if dominant trait is homozygous dominant or heterozygous
principles of heredity
- law of segregation
- law of independent assortment
allele
alternate form of a gene
Mendel 4 concepts
- Alternative versions of genes account for
variations in inherited characteristics - For each character, an organism inherits
two alleles of a gene, one from each parent. - If two alleles at a locus differ, then the dominant allele
determines the appearance and the recessive allele
has no noticeable effect - Law of segregation: the two alleles for the same trait
separate during gamete formation and end up in
different gametes
law of segregation
the two alleles for the same trait separate during gamete formation and end up in different gametes
Monohybrid crosses
a cross between the F1 hybrids
law of independent assortment
genes for one trait are not inherited with genes of another trait
- This law only applies to: genes that are located on
different chromosomes (not homologous) OR
genes that are very far apart on the same
chromosome
a heterozygous dyhybrid will produce what ratio?
Produces a 9:3:3:1 phenotypic ratio
if a trait is x-linked then
males are more commonly affected than females
Many traits do not follow the ratios predicted by Mendel’s law why?
- varying degrees of dominance
- many traits are produced through multiple genes acting together
- some traits are determined by genes on the sex chromosomes
- some genes are adjacent or close to one another on the same chromosome and will segregate as a unit
- some traits are a result of non-nuclear inheritance (chloroplast n mitochondria)
incomplete dominance
- neither allele is fully dominant
- F1 generation has a phenotype that is mix with the parental generation
- ex: red with white will produce pink offspring
codominance
- two alleles that affect phenotype are both expressed
- human blood group
- type AB blood- A and B are both expressed
multiple alleles
genes that exist in forms with more than two alleles
- human blood type- iA, iB, i
epistasis
the phenotypic expression of a gene at one locus affects a gene at another locus
- ex: coat color in labs and some mice
sex linked genes
genes found on either x or y chromosome
fathers can pass x linked alleles to all ____ but none of their ____
and
mother can pass x linked alleles to _____
- daughters, sons
- both daughter and sons
if an x-linked trait is due to a recessive allele.
- females will only express trait is they’re homozygous
- Because males only have one X chromosome,
they will express the trait if they inherit it from
their mother
■ They are called hemizygous (since the term
heterozygous does not apply)
■ Due to this males are much more likely to have
an X-linked disorder
name the 3 x-linked disorders
- duchenne muscular dystrophy: progressive weakening of muscles
- hemophilia: inability to properly clot blood
- color blindness: inability to correctly see colors
the inactive x in each cell of a female condenses into a __
Barr body (helps regulate gene dosage in females
tay-sachs disease
- autosomal recessive disease
- mutated HEXA gene
- body fails to produce an enzyme that breaks down lipids
- affects the nervous system and leads to blindness
sickle cell anemia
- autosomal recessive disease
- sickle cells contain abnormal hemoglobin molecules
- mutated HBB gene
non-disjunction
chromosomes are unable to separate properly during meoisis I or II
- karyotypes can detect this
ex: down syndrome: three copies of chromosome 21
