Meiosis Biology 2017

Homologous Chromosomes These are chromosomes that carry genes (alleles) for the same traits in the same order. You get one from mom and one from dad. The next slide has a line up of the 22 pairs of homologous chromosomes known as autosomes and the pair of sex chromosomes.

Karyotypes To look at homologous chromosomes, scientists use karyotypes. These are pictures of the pairs of homologous chromosomes lined up, the one from mom is next to the one from dad.

Human Female Karyotype

Human Male Karyotype

Meiosis Meiosis produces sex cells and reduces the number of chromosomes to one half the amount found in a body cell. Human body cells have 46 chromosomes so sex cells have 23. When sperm and egg unite, 23 + 23 = 46. This brings the newly formed zygote back to a full complement of chromosomes.

Meiosis

Crossing Over

Meiosis I and Meiosis II

Correct Meiosis

Meiosis Overview

Correct Meiosis

Metaphases

Correct Meiosis

Non-Disjunction When chromosomes don’t divide evenly in Meiosis I or Meiosis II.

Non-disjunction or mistakes in meiosis

Down’s Syndrome A Down’s Syndrome individual has (3) #21 chromosomes instead of 2. This is called a trisomy. Individuals with Down’s Syndrome have a reduced mental capacity, are short in stature, have fat pads under their eyes that make them resemble people from Mongolia. At one time people who had Down’s Syndrome where referred to as Mongoloids.

Down’s Syndrome Karyotype

Individuals with Down’s Syndrome

Turner’s Syndrome A Turner’s Syndrome female has only one X chromosome instead of 2. This is known as a monosomy. Turner’s Syndrome is only present in females. They will be short in height, mentally normal, but can’t have children as they are sterile. They also often have webbed necks and chests that resemble a shield.

Turner’s Syndrome

Individuals with Turner’s Syndrome

Klinefelter’s Syndrome Klinefelter’s individuals are all male and have at least two X chromosomes instead of 1 along with their Y chromosome. They have narrow shoulders, wide hips, enlarged breast tissue, extra long arms and are often mentally handicapped. Their genitals are often small, however they can reproduce.

Klinefelter’s Syndrome

Body shape of Klinefelter’s individual

Poly-X Klinefelter’s Syndrome Males with poly-X Klinefelter syndrome have more than one extra X chromosome, so their symptoms might be more pronounced than in males with KS. In childhood, they may also have seizures, crossed eyes, constipation, and recurrent ear infections. Poly-KS males might also show slight differences in other physical features. Some common additional symptoms for several poly-X Klinefelter syndromes are listed below.

48,XXYY Tetrasomy Long legs Little body hair Lower IQ, average of 60 to 80 (normal IQ is 90 to 110) Leg ulcers and other vascular disease symptoms Extreme shyness, but also sometimes aggression and impulsiveness

48,XXXY (or tetrasomy) Eyes set further apart Flat nose bridge Arm bones connected to each other in an unusual way Short Fifth (smallest) fingers curve inward (clinodactyly, pronounced KLAHY-noh-dak-tl-ee) Lower IQ, average 40 to 60 Immature behavior

49,XXXXY (or pentasomy) Low IQ, usually between 20 and 60 Small head Short Upward-slanted eyes Heart defects, such as when the chambers do not form properly High feet arches Shy, but friendly Difficulty with changing routines

Polyploidy Have more than normal sets of chromosomes Is rare in animals and results in death Occurs in plants, creating larger, healthier plants Examples: Triploid (3 chromosomes/set) Tetrapoid (4 chromosomes/set)

Haploid to Tetraploid

Polyploid Plants

Polyploidy in Plants Polyploid organisms have multiple sets of the genome. For example, a strawberry normally has 7 pairs or 14 chromosomes. When a strawberry is polyploid, it can have up to 8 full sets of its genome equaling 56 chromosomes.

Effect of Polyploidy in Plants Increases fruit weight, fruit size, seed size, crop load and flower size Can be used to create a higher diversity Increase bloom period Creates stronger plants

Chrysanthemums

Beneficial Mistakes

How Polyploid Strawberries Are Created

Strawberries

Polyploid vs. Dipolid