Biology unit 2 part 1
what is Locus
Chromosomal position where DNA for a specific gene "lives"
What would be true if linkage of two genes was complete?
Crossing over between the two genes would never occur.
what is Alleles
Different forms of a gene
A disorder caused by nondisjunction of chromosome 21, resulting in a trisomy 21 child, is
Down syndrome.
what is a the way we behave and look called?
phenotype.
Human eye color is the result of
polygenic inheritance
When alleles on homologous chromosomes move into different gametes during meiosis, this demonstrates
segregation.
In humans, the sex of the offspring is determined by the
sex chromosome carried by the sperm cell
Traits controlled by sex-linked recessive genes are expressed more often in males because
the male has only one gene for the trait
What is the reason for the prevalence of the sickle-cell allele in African populations?
Heterozygotes have some resistance to the parasite that causes malaria
what does Genome refer to?
all standard loci for a species
Mendel's "units" are now called
genes
The genetic makeup of an individual is the
genotype.
According to the law of segregation, in an organism with the genotype Aa
half the gametes have A and half have a.
what is Incomplete dominance
heterozygote displays intermediate trait
When the two gametes that fuse to form a zygote contain different alleles of a given gene, the offspring is
heterozygous.
A human sperm cell possesses autosomes and
either an X or a Y chromosome
what is Gene
A segment of chromosomal DNA controlling a specific trait
what is Trait
A variable characteristic of organism
what does Recessive mean
Allele is not expressed in heterozygote
what does Dominant mean
Allele that is expressed 100% in heterozygote
what is Heterozygous
Maternal & paternal alleles differ.
what is Homozygous
Maternal & paternal alleles same
What is the difference between phenotype and genotype?
Phenotype is the physical expression of a trait and genotype is the combination of alleles carried by the organism
When a single gene has multiple effects on phenotype
Pleiotropy
a single trait is influenced by several genes interacting
Polygenic inheritance
What type of allele produces its effects in only homozygous individuals
Recessive
Which of the following is true of genes that are found near each other on the same chromosome?
They are linked and tend to be inherited together.
Which of the following conditions may cause infertility in a human?
XXY
Codominance occurs when
both of the alleles in a heterozygote are expressed phenotypically in an individual.
When genes are linked, a few of the recombinant genotypes still occur in the offspring because of
crossing over.
If, in a heterozygous individual, only one allele is expressed in the phenotype, that allele is
dominant.
According to the law of segregation when do pairs of alleles separate
during the formation of gametes.
The failure of chromosomes to segregate properly during meiosis is called
nondisjunction.
A recessive allele is one
whose effect is masked by a dominant allele
