Genetics vocabulary | Inheritance and variation | Middle school biology | Khan Academy

Summary

This video explains the basics of genetics, focusing on how sexually reproducing organisms inherit DNA from both parents. It covers the structure of chromosomes and how they relate to genes and alleles. The video differentiates between genotype (the genetic makeup) and phenotype (the expressed traits), and explains dominant and recessive alleles. It also introduces the concepts of homozygous (same alleles) and heterozygous (different alleles) genotypes, providing a foundational understanding of how genetic traits are inherited and expressed.

Takeaways

• 🧬 Human beings have 23 pairs of chromosomes, with each pair consisting of one chromosome from the male parent and one from the female parent.
• 🌟 Chromosomes are made up of DNA strands and other packaging materials, which contain genes that code for various traits.
• 🔍 Genes are segments of DNA that code for specific proteins, which can influence traits such as height, hair color, and eye color.
• 🔄 Each chromosome in a pair generally codes for the same genes, meaning there are regions on each that code for the same traits.
• 🧬 Alleles are different versions of a gene, which can result in different expressions of a trait, such as different hair colors.
• 🔑 Knowing the alleles an organism has allows us to determine its genotype, which is the genetic makeup for a particular trait.
• 👀 The phenotype is the observable expression of a trait, such as hair color, which can be influenced by the underlying genotype.
• 🏳️‍🌈 Dominant alleles can mask the expression of recessive alleles, meaning that just one dominant allele can result in the dominant phenotype.
• 🎲 There are various genotypes that can result in the same phenotype, depending on whether alleles are dominant or recessive.
• 🔄 Homozygous refers to having two identical alleles for a gene, while heterozygous means having two different alleles.
• 📚 Understanding these genetic concepts allows for a deeper discussion and analysis of genetics and inheritance patterns.

Q & A

How do sexually reproducing organisms, including humans, receive their DNA?

Sexually reproducing organisms, including humans, receive DNA from both their male and female parents. Humans have 23 pairs of chromosomes, with one chromosome of each pair coming from each parent.

What are chromosomes and what do they consist of?

Chromosomes are structures that contain DNA tightly coiled around proteins. They are composed of DNA and other molecules that help package and protect the genetic information.

What is the relationship between DNA, genes, and traits like height or hair color?

DNA contains segments that code for different genes. These genes can be translated into proteins, which in turn influence traits such as height, hair color, eye color, and many other physical and functional characteristics.

How can the same gene have different effects on an organism's traits?

The same gene can have different versions called alleles, which can result in different expressions of traits. For example, different alleles for hair color can result in blonde or brown hair.

What is an allele and how does it relate to genes?

An allele is a version of a gene. Each gene can have multiple alleles, which may code for different characteristics of the same trait, such as different hair colors.

What is meant by an organism's genotype?

An organism's genotype refers to the specific set of alleles it has for a particular gene or set of genes. Knowing the alleles an organism has allows us to determine its genotype.

How is an organism's phenotype different from its genotype?

The phenotype is the observable expression of an organism's traits, such as hair color, while the genotype is the genetic makeup that determines these traits. The phenotype is what you can see, while the genotype is what you can infer from the organism's genetic code.

What is the difference between a dominant and a recessive allele?

A dominant allele is one that will express its trait even if only one copy is present, while a recessive allele will only express its trait if two copies are present. In the context of the script, the brown hair allele is considered dominant over the blonde hair allele.

Can you explain the terms homozygous and heterozygous in relation to genotypes?

Homozygous refers to a genotype where both alleles for a gene are the same, while heterozygous refers to a genotype where the alleles are different. For example, having two dominant alleles (BB) or two recessive alleles (bb) makes an organism homozygous for that gene, whereas having one dominant and one recessive allele (Bb) makes it heterozygous.

How can different genotypes result in the same phenotype?

Different genotypes can result in the same phenotype if the dominant allele masks the expression of the recessive allele. For instance, both BB and Bb genotypes could result in a brown hair phenotype if the brown allele is dominant.

What is the simplest way to get a recessive phenotype, such as blonde hair in the given scenario?

The simplest way to get a recessive phenotype, like blonde hair, is to have two copies of the recessive allele (bb), which would then be expressed because there is no dominant allele to mask it.