Heredity

DNA

  • All living things are composed of cells that promote growth and sustain life according to instructions in their molecules of DNA

  • DNA (deoxyribonucleic acid)

    • A molecule that contains the chemical instructions for cells to manufacture various proteins

    • Promotes growth and sustains life

  • Chromosomes

    • A long DNA molecule coiled around proteins

    • Consists of 46 chromosomes arranged in 23 pairs

    • Contains all of our genes

Genes

  • A small section on a chromosome that tells cells what proteins to produce

  • Genomes involve the full set of genes that are the instructions to make an individual member of a certain species

  • Genes are similar, but what makes us unique?

  • Made up of DNA

Male or Female

  • Humans usually possess 46 chromosomes

    • 44 autosomes and 2 sex chromosomes

  • 23rd pair determines sex

    • XX - Female

    • XY - Male

  • Historically, male offspring were preferred

    • Women were blamed initially

  • Ways to make male children…

    • Greek husbands tied left testicle off and women would lie on their right side

    • Try and guess an ovulation schedule

    • Weather

  • Ways to prevent female birth

    • Inactivating X sperm before conception

    • In vitro fertilization (IVF)

    • Aborting XX fetuses

Assisted Reproduction

  • Assisted Reproductive Technology (ART)

    • General term for the techniques designed to help infertile couples conceive and sustain a pregnancy

  • In Vitro Fertilization (IVF)

    • Involves fertilization that takes place outside a woman’s body

    • Involves mixing sperm with surgically removed ova from the woman’s ovary and implanting zygote into a woman’s uterus

Siblings + Twins

  • Monozygotic (Identical) Twins

    • Originates from one zygote that splits apart very early in development

    • Incomplete split results in conjoined twins

    • Same genotype but slight variations in phenotype are possible due to environmental influences

  • Dizygotic (fraternal) Twins

    • Result from the fertilization of two separate ova by two separate sperm

    • Dizygotic twins have half their genes in common and occur twice as often as monozygotic twins

    • Incidence is genetic and varies by ethnicity and age

  • Adoption studies (compared to twin studies) suggest the adoptees tend to be more different from their adoptive parents and siblings than their biological parents

  • Adoptees bear more resemblance in their outgoingness and agreeableness to their biological parents than to their adoptive parents

  • Two adopted children in the same home bear no more resemblance to each other than kids from two separate families

  • These studies strongly point to the simple fact that biologically related children turn out to be different in a family

Parenting

  • Parenting does affect biologically related and unrelated children

  • Parent influences…

    • Attitudes, values

    • Manners, beliefs

    • Faith, politics

Heritability

  • Refers to the extent to which the differences among people are attributable to genes

  • There’s a 90% difference in people’s height that’s attributed to their genes

Gene-Environment Correlation

  • Passive

    • Bio-parents directly pass on genes to their kids

    • Bio-parents also pass on home environments that are influenced by their own heritable characteristics

    • Parents provide/guide child’s interests

  • Evocative (reactive)

    • Gene-environment correlation happens when an individual’s genetic makeup evokes an environmental response

    • Some traits elicit more adult responses

  • Active

    • Occurs when an individual possesses a heritable propensity to select environmental exposure

    • Child seeks/selects favorable environments

Additive Heredity

  • Additive genes are interactions among genes and alleles whose effects add something to some aspect of the phenotype

    • Effects of additive genes add up to make the phenotype

Gene-Gene Interactions

  • Dominant-recessive heredity

    • Dominant gene can completely control the phenotype with no noticeable effect of the recessive gene

    • Dominant gene is far more influential than the recessive gene (non-additive)

    • Effect of recessive genes can sometimes be noticed

  • X-Linked

    • Special case of dominant-recessive pattern

    • Gene carried on the X chromosome

Chromosomal and Genetic Problems

  • Some gametes have more or fewer than 23 chromosomes

    • Sometimes only part of the 23rd chromosome is missing

  • Down syndrome

    • Called trisomy-21 because the person has three copies of chromosome 21

    • Involves around 300 distinct characteristics from the third chromosome; unique individuals

  • Dominant disorders

    • 7k known single-gene disorders are dominant

    • Evident in phenotype

    • Rare because people rarely live long enough to reproduce

    • Some exceptions include Huntington disease and Alzheimer’s disease

  • Recessive disorders

    • More numerous because they are passed down from one gen to the next by carriers who are unaware of their genotype

  • Fragile X Syndrome

    • Caused by more than 200 repetitions of one triplet on one gene

    • Most common form of inherited form of inherited mental retardation

  • Sickle-Cell trait

    • Offers some protection against malaria

    • African carriers are more likely than non-carriers to survive

  • Cystic fibrosis

    • More common among people with northern European ancestors

    • Carriers may have been protected against cholera

    • Most common genetic disorder among white people

Nature and Nurture

  • Alcohol Use Disorder

    • Involves alleles that create an addictive pull

    • Is genetic but is also much more personal

  • Nearsightedness

    • Limited focus at birth; change in eyeball shape at puberty; decreasing myopia at middle age

    • Genes: Heritability of about 75%

    • Social context

      • Environment (time indoors and reading)

      • Homework and lack of play