NAS 2 Heredity

Meiosis

reduces the chromosome number by half to produce four genetically diverse haploid gametes (sperm or egg cells).

Meiosis I

Homologous chromosomes are separated into two daughter cells, including processes such as crossing over and independent assortment.

Difference between meiosis I and meiosis II

Meiosis I separates homologous chromosomes, while meiosis II separates sister chromatids, resulting in four haploid cells.

Prophase I

Homologous chromosomes pair up and undergo crossing over, where sections of chromatids are exchanged between chromosomes, increasing genetic diversity.

Metaphase I

Homologous chromosome pairs line up along the middle and spindle fibers attach to the centromeres.

Anaphase I

Homologous chromosomes are pulled to opposite poles of the cell, but sister chromatids remain attached.

Telophase I

The separated chromosomes reach the poles, and two daughter cells are formed, each with half the number of chromosomes.

Meiosis II

Resembles mitosis; the sister chromatids are separated, resulting in four haploid gametes.

Prophase II

Chromosomes condense, and new spindle fibers form in each of the two daughter cells.

Metaphase II

Chromosomes align along the metaphase plate in both daughter cells.

Anaphase II

The centromeres split, and sister chromatids are pulled to opposite poles of the cells.

Telophase II

The separated chromatids are now individual chromosomes, and four haploid cells are formed.

Difference between meiosis and mitosis

Meiosis results in four genetically unique haploid cells with half the chromosome number, while mitosis results in two identical diploid cells with the same chromosome number.

Genetic variation

Crossing over during prophase I, independent assortment during metaphase I, and random fertilization all contribute to ____ in the resulting haploid gametes.

Crossing over

The exchange of genetic material between homologous chromosomes during prophase I, creating new combinations of alleles.

Independent assortment

Occurs during metaphase I, when the homologous chromosomes align randomly at the metaphase plate, leading to a variety of possible combinations of chromosomes in the gametes.

Genetically unique gametes

Produced through crossing over, independent assortment, and the random nature of fertilization.

Genotype

Refers to the genetic makeup of an individual (the alleles they inherit).

Phenotype

Refers to the physical expression or traits that result from the genotype.

Alleles

Different versions of a gene that determine traits by interacting with each other.

Dominant allele

will express its trait even if only one copy is present in the genotype

Recessive allele

only expresses its trait when two copies are present in the genotype

Mendel's key experiments

Involved crossbreeding pea plants to study how traits like flower color, seed shape, and plant height were inherited.

Mendel's conclusions

Traits are inherited as discrete units (genes), and these units follow predictable patterns of inheritance (dominant/recessive).

Mendel's law of segregation

States that allele pairs separate during gamete formation, and randomly unite at fertilization.

Mendel's law of independent assortment

States that genes for different traits are inherited independently of each other, as long as they are on different chromosomes.

Punnett square

A diagram used to predict the genetic outcomes of a cross between two organisms.

Autosomal dominant disorders

Caused by a dominant allele; a person only needs one copy of the dominant allele to express the disorder (ex: Huntington’s disease)

Autosomal recessive disorders

Caused by recessive alleles; a person must inherit two copies of the recessive allele (one from each parent) to express the disorder (ex: cystic fibrosis).

Sex-linked genetic disorder

Caused by an allele on the X or Y chromosome; most are X-linked, more common in males who have only one X chromosome (ex: hemophilia, color blindness).

Genotype for a carrier of a recessive disorder

Has one dominant and one recessive allele (heterozygous) and does not express the disorder but can pass the recessive allele to offspring.

Nondisjunction

The failure of chromosomes or chromatids to separate properly during cell division, leading to an abnormal number of chromosomes in the resulting gametes.

Trisomy

A condition where an individual has three copies of a chromosome instead of the usual two, such as in Down syndrome

Monosomy

A condition where an individual has only one copy of a chromosome instead of the usual two, such as in Turner syndrome

Inversions in chromosome structure

Occur when a section of a chromosome is reversed end to end, which can lead to problems in chromosome pairing during meiosis.

Inversions and genetic material

May disrupt the function of genes in the affected region and cause issues during crossing over in meiosis, potentially leading to genetic disorders.

Translocations in chromosome structure

Occur when a segment of one chromosome breaks off and attaches to another chromosome, which can lead to unbalanced genetic material in the offspring.

Translocations and genetic material

Can result in a loss or gain of genetic material, which may cause genetic disorders or cancer if vital genes are disrupted.

Reciprocal translocation

Occurs when two non-homologous chromosomes exchange segments, and it can lead to fertility issues or disorders if important genes are disrupted.

Inversions and translocations affecting meiosis

Can cause improper chromosome alignment during meiosis, leading to genetic imbalances and potential infertility or developmental disorders.