Chap 10 Patterns of Inheritance Flashcards
What does DNA do with our genes?
carries our genes
What is a gene?
a portion of DNA whose sequence of nucleotides (A,C,G,T) encodes a protein
What determine many of an organisms’s characteristics?
the proteins expressed in cells - e.g. eye, hair, skin color
What are chromosomes?
packets of genetic information
Describe the structure of a chromosome.
long strands of DNA wrapped around histone proteins
How many genes are in a chromosome?
lots
When are chromosomes passed on?
during cell division
How many chromosomes do humans have?
46 (23 from each parent when male and female gamete fuses at fertilization)
How are chromosomes paired (type of cell)?
in diploid cells
The zygote is what after fertilization?
diploid
What does it mean when a cell is diploid?
it has two sets of chromosomes
Each chromosome is a member of what?
a homologous pair
Meiosis does what to homologous pairs?
separates them
Diploid cells have what for each gene?
two alleles
Alleles might be…?
identical or different
Who discovered the basic law of inheritance?
Gregor Medel
What did Gregor Mendel use to study heredity?
pea plants
Why did Gregor Mendel use pea plants to study heredity?
it is easy to control which plant mates with which, and he was able to set up systematic breeding experiments
What gave Mendel clues about the genes of parents?
offspring
True-breeding plants produce what?
produce offspring identical to themselves
Hybrid plant produce what?
(outwardly resemble true-breeders) but produce mixed offspring
Are some alleles dominant?
yes
Dominant alleles do what?
exert their effects whenever they are present (yellow seed)
Are some alleles recessive?
yes
Recessive alleles do what?
its effect is masked if a dominant allele is also present (green seed)
Recessive alleles often do what?
encode nonfunctional proteins
Why do some plants produce both yellow and green seeds?
because each plant has two alleles for each gene (because of their homologous pairs of chromosomes)
May homologous chromosomes have different alleles?
yes
What does a genotype represent?
an individual’s two alleles for one gene
What does it mean when a genotype is Homozygous dominant?
individuals have two dominant alleles for a gene
What does it mean when a genotype is heterozygous?
individuals have one dominant and one recessive allele
What does it mean when a genotype is homozygous recessive?
individuals have two recessive alleles
What is the genotype responsible for?
the phenotype
What is a phenotype?
the physical appearance - e.g. observable characteristic like seed color
How is the phenotype determined?
by how the alleles interact with each other
How do you determine the genotype of a parent?
by looking at the offspring
Can individuals with the dame phenotype have different genotypes?
yes
How do genotypes lead to phenotypes (seeds)?
the seed color gene encodes a pigment-metabolizing enzyme
allele Y encodes an active enzyme, producing yellow pigment
due to a mutation, allele y encodes and inactive enzyme that does not produce yellow pigment
What represents gamete formation and fertilization?
Punnett squares
What does a Punnett square do?
uses the genotypes of the parents to reveal which alleles the offspring may inherit
Explain Homozygous dominant with seeds.
if a cross between a yellow-seed pea plant an d a green-seed pea plant yields all yellow seeds… then the yellow-seed parent must be homozygous dominant (YY)
Explain Heterozygous with seeds?
if a cross between a yellow-seed pea plant and a green-seed pea plant yields some green seeds… then the yellow-seed parent must be heterozygous (Yy)
Punnett squares is prediction showing what?
the relative proportion of the offspring’s phenotypes and genotypes
Mendel deduced what?
the law of segregation
What is the law of segregation?
two alleles of each gene “segregate” (move apart from each other), during gamete formation
Punnet squares can be used to track what?
the inheritance of genetic disorders - e.g. cystic fibrosis
What tracks the inheritance of two genes at once?
dihybrid crosses
What do dihybrid crosses do?
track the inheritance of two genes at once
What can be shown on one large Punnett square?
two genes on different chromosomes (the alleles for each gene are shown in the parent, gametes, and offspring)
Meiosis explains what?
the law of independent assortment
What is the law of independent assortment?
chromosomes (carrying alleles) are packaged into gametes independently of each other as the spindle pulls them into place
How are genes on different chromosomes are inherited?
inherited separately
Why can we predict the genotype and phenotype ratios of the offspring?
because chromosomes are assorted independently
How are genes on the same chromosome inherited?
inherited together
What is different when chromosomes are inherited together?
different ratios will be seen in offspring
Genes that are physically near each other on the same chromosome are what?
linked/inherited together
When can genes become “unlinked”?
during cross over
What does crossing over do to linked genes?
physically separates the two genes onto two different chromosomes
Do all genes follow Mendelian inheritance patterns?
no
What creates a new phenotype?
incomplete dominance
The way alleles interact changes what?
the nature of the phenotypes but not the genotypes
Give an example of incomplete dominance?
Red and White alleles can make pink
Can one gene influence many phenotypes?
yes
What is pleiotropy?
one gene has multiple effects on the phenotype - e.g. a gene might affect more than one biochemical pathway, e.g. marfan syndrome
What type of genes have unique inheritance patterns?
sex-linked
What is a sex-linked gene?
phenotypes that affect one sex more than the other (that is, the alleles controlling them are on the X or Y chromosome)
How many alleles for X-linked genes do males have?
one
How many alleles for X-linked genes do females have?
two
Does the Y chromosome have alleles for X-linked genes?
No
Which allele is expressed for the X on males?
whichever allele males have on their single X chromosome is the one that is expressed as a phenotype
What prevents double dosing of gene products?
X-inactivation
Each cell does what to prevent double dosing of gene products?
each cell in an XX individual randomly inactivates one X chromosome (the genes on the inactivated chromosomes won’t be used to produce proteins)
What can alter a phenotype?
the environment (e.g. siamese cats have a mutation in a gene for an enzyme responsible for pigment production in their fur. the mutates enzymes is active only in cool body parts, while in warm body parts the mutated enzyme is inactive and no color is produced. Thus the cats have black paws, face, ears, and tail while the rest of the body is colorless)
